Do not apply magic unnecessarily for nocase

If the pattern part's upper and lower case forms are identical, then
nocase has no effect, and there's no need to turn it into a regular
expression.

Not sure if this is related to #178, but it seems like it may be.

minimatch.js

@@ -427,7 +427,7 @@ class Minimatch {
     if (pattern === '') return ''
 
     let re = ''
-    let hasMagic = !!options.nocase
+    let hasMagic = false
     let escaping = false
     // ? => one single character
     const patternListStack = []
@@ -750,6 +750,11 @@ class Minimatch {
       return [re, hasMagic]
     }
 
+    // if it's nocase, and the lcase/uppercase don't match, it's magic
+    if (options.nocase && !hasMagic) {
+      hasMagic = pattern.toUpperCase() !== pattern.toLowerCase()
+    }
+
     // skip the regexp for non-magical patterns
     // unescape anything in it, though, so that it'll be
     // an exact match against a file etc.

tap-snapshots/test/basic.js.test.cjs

@@ -162,7 +162,7 @@ exports[`test/basic.js TAP basic tests > makeRe X* 2`] = `
 `
 
 exports[`test/basic.js TAP basic tests > makeRe XYZ 1`] = `
-/^(?:(?=.)XYZ)$/i
+/^(?:XYZ)$/i
 `
 
 exports[`test/basic.js TAP basic tests > makeRe [ 1`] = `

test/nocase-magic.js

@@ -0,0 +1,13 @@
+const t = require('tap')
+const { Minimatch } = require('../')
+
+const nomagic = '../1/2/3'
+const yesmagic = '../x'
+
+t.same(new Minimatch(nomagic, { nocase: true }).set, [
+  [ '..', '1', '2', '3']
+])
+
+t.same(new Minimatch(yesmagic, { nocase: true }).set, [
+  ['..', /^x$/i]
+])