Handling GeometryTileWorker edge cases:

 - If redoLayout completes without a placementConfig, move to NeedPlacement
 - If setPlacementConfig called while in NeedPlacement, attemptPlacement
 - If setPlacementConfig called while in NeedLayout and there are not other dependencies, attemptPlacement

The idea with these changes is that waiting on the first placementConfig is essentially similar to a symbol dependency, and we need to make sure we do layout/placement in response to it being satisfied. However, we only want to trigger activity the first time, to avoid short circuiting the coalescing logic.

 - Don't re-trigger layout when symbol dependencies arrive unless all of our prior dependencies have been satisfied first

This avoids a case where we can have multiple "different" sets of dependencies in flight at the same time, and we could end up rendering with the wrong set.

src/mbgl/tile/geometry_tile_worker.cpp

@@ -122,6 +122,7 @@ void GeometryTileWorker::setLayers(std::vector<std::unique_ptr<Layer>> layers_,
 
 void GeometryTileWorker::setPlacementConfig(PlacementConfig placementConfig_, uint64_t correlationID_) {
     try {
+        bool firstPlacement = !placementConfig;
         placementConfig = std::move(placementConfig_);
         correlationID = correlationID_;
 
@@ -135,7 +136,14 @@ void GeometryTileWorker::setPlacementConfig(PlacementConfig placementConfig_, ui
             break;
 
         case NeedPlacement:
+            if (firstPlacement) {
+                attemptPlacement();
+            }
+            break;
         case NeedLayout:
+            if (firstPlacement && !hasPendingSymbolDependencies()) {
+                redoLayout();
+            }
             break;
         }
     } catch (...) {
@@ -196,7 +204,12 @@ void GeometryTileWorker::coalesced() {
             break;
 
         case NeedLayout:
-            redoLayout();
+            if (!hasPendingSymbolDependencies()) {
+                // Don't re-trigger layout if we have outstanding symbol dependencies
+                // Redoing layout could invalidate the outstanding dependencies, but
+                // when they arrived we would treat them as valid
+                redoLayout();
+            }
             break;
 
         case NeedPlacement:
@@ -234,7 +247,6 @@ bool GeometryTileWorker::hasIconDependencies(const IconDependencyMap &iconDepend
 
 void GeometryTileWorker::redoLayout() {
     if (!data || !layers) {
-        // Waiting for initial configuration
         return;
     }
 
@@ -333,7 +345,7 @@ void GeometryTileWorker::redoLayout() {
         correlationID
     });
 
-    if (hasPendingSymbolDependencies()) {
+    if (!placementConfig || hasPendingSymbolDependencies()) {
         state = NeedPlacement;
     } else {
         attemptPlacement();