Sequence Diagram Activations error

[securitygeneration]

Describe the bug
Deactivating an inactive Participant throws an uninformative error. With complex flows that have lots of activations and deactivations, it can be easy to get lost with which are active at any given point in time. Some indication as to which line threw the error would be useful.

To Reproduce
The following code:

sequenceDiagram
  participant user as End User
  participant Server as Server
  participant System as System
  participant System2 as System2

user->>+Server: Test
user->>+Server: Test2
user->>System: Test
Server->>-user: Test
Server->>-user: Test2

%% The following deactivation of Server will fail
Server->>-user: Test3

Produces error:

(node:7060) UnhandledPromiseRejectionWarning: Error: Evaluation failed: TypeError: Cannot read property 'starty' of undefined
    at file:///usr/local/lib/node_modules/mermaid.cli/mermaid.min.js:1:720952
    at file:///usr/local/lib/node_modules/mermaid.cli/mermaid.min.js:1:721054
    at Array.forEach (<anonymous>)
    at Object.e.draw (file:///usr/local/lib/node_modules/mermaid.cli/mermaid.min.js:1:720350)
    at Object.render (file:///usr/local/lib/node_modules/mermaid.cli/mermaid.min.js:1:760928)
    at s (file:///usr/local/lib/node_modules/mermaid.cli/mermaid.min.js:8:233)
    at Object.init (file:///usr/local/lib/node_modules/mermaid.cli/mermaid.min.js:8:318)
    at __puppeteer_evaluation_script__:17:20
    at ExecutionContext._evaluateInternal (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/ExecutionContext.js:122:13)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async ExecutionContext.evaluate (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/ExecutionContext.js:48:12)
    at async ElementHandle.evaluate (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/JSHandle.js:55:12)
    at async ElementHandle.$eval (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/JSHandle.js:478:20)
  -- ASYNC --
    at ExecutionContext.<anonymous> (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/helper.js:111:15)
    at ElementHandle.evaluate (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/JSHandle.js:55:42)
    at ElementHandle.<anonymous> (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/helper.js:112:23)
    at ElementHandle.$eval (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/JSHandle.js:478:40)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
  -- ASYNC --
    at ElementHandle.<anonymous> (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/helper.js:111:15)
    at DOMWorld.$eval (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/DOMWorld.js:156:21)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
  -- ASYNC --
    at Frame.<anonymous> (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/helper.js:111:15)
    at Page.$eval (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/Page.js:347:29)
    at Page.<anonymous> (/usr/local/lib/node_modules/mermaid.cli/node_modules/puppeteer/lib/helper.js:112:23)
    at /usr/local/lib/node_modules/mermaid.cli/index.bundle.js:83:14
    at Generator.next (<anonymous>)
    at step (/usr/local/lib/node_modules/mermaid.cli/index.bundle.js:4:191)
    at /usr/local/lib/node_modules/mermaid.cli/index.bundle.js:4:361
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
(node:7060) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:7060) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Expected behavior
A more useful error message stating possibly Invalid participant deactivation on line x

[knsv]

I can see how this could be a problem. I will take a look at this.