fix: handle void to void during convertExpression (#2412)

Author: HerrCai0907

Diff for: src/compiler.ts

@@ -3436,9 +3436,13 @@ export class Compiler extends DiagnosticEmitter {
   ): ExpressionRef {
     var module = this.module;
 
-    // void to any
     if (fromType.kind == TypeKind.VOID) {
-      assert(toType.kind != TypeKind.VOID); // convertExpression should not be called with void -> void
+      if (toType.kind == TypeKind.VOID) {
+        // void to void: Can happen as a result of a foregoing error. Since we
+        // have an `expr` here that is already supposed to be void, return it.
+        return expr;
+      }
+      // void to any
       this.error(
         DiagnosticCode.Type_0_is_not_assignable_to_type_1,
         reportNode.range, fromType.toString(), toType.toString()

Diff for: tests/compiler/variable-access-in-initializer.json

@@ -3,6 +3,7 @@
   ],
   "stderr": [
     "TS2448: Variable 'variable-access-in-initializer/a' used before its declaration.",
+    "TS2448: Variable 'variable-access-in-initializer/c' used before its declaration.",
     "TS2448: Variable 'variable-access-in-initializer/test~b' used before its declaration.",
     "EOF"
   ]

Diff for: tests/compiler/variable-access-in-initializer.ts

@@ -1,4 +1,5 @@
 var a = (a = 4, 3); // TS2448
+let c = typeof c;
 
 function test(): void {
   let b = (b = 4, 3); // TS2448