Fix flow assertion on invalid function expression

src/flow.ts

@@ -1193,7 +1193,6 @@ export class Flow {
   canOverflow(expr: ExpressionRef, type: Type): bool {
     // TODO: the following catches most common and a few uncommon cases, but there are additional
     // opportunities here, obviously.
-    assert(type != Type.void);
 
     // types other than i8, u8, i16, u16 and bool do not overflow
     if (!type.isShortIntegerValue) return false;

tests/compiler/function-expression-error.json

@@ -0,0 +1,8 @@
+{
+  "asc_flags": [
+  ],
+  "stderr": [
+    "TS1110: Type expected.", "missingReturnType",
+    "EOF"
+  ]
+}

tests/compiler/function-expression-error.ts

@@ -0,0 +1,5 @@
+// see: https://github.com/AssemblyScript/assemblyscript/issues/2036
+
+const missingReturnType: u32 = (() => 42).index;
+
+ERROR("EOF");