[test] Add regression test for already fixed syntax coloring crash (rdar31960764)

Author: Nathan Hawes

test/IDE/coloring_unclosed_hash_if.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-ide-test -syntax-coloring -source-filename %s | %FileCheck %s
+// RUN: %target-swift-ide-test -syntax-coloring -typecheck -source-filename %s | %FileCheck %s
+
+// CHECK: <#kw>#if</#kw> <#id>d</#id>
+// CHECK-NEXT: <kw>func</kw> bar() {
+// CHECK-NEXT: <#kw>#if</#kw> <#id>d</#id>
+// CHECK-NEXT: }
+// CHECK-NEXT: <kw>func</kw> foo() {}
+
+#if d
+func bar() {
+  #if d
+}
+func foo() {}