[Fuzzer] Do not make local.get without function context (#7813)

The fuzzer tries to finish quickly by falling back to creating
local.gets or constants after it reaches the end of its random input.
The former option should only be used inside a funtion context, though.

Author: tlively

src/tools/fuzzing/fuzzing.cpp

@@ -2066,12 +2066,13 @@ Expression* TranslateToFuzzReader::make(Type type) {
       nesting >= 5 * fuzzParams->NESTING_LIMIT || // hard limit
       (nesting >= fuzzParams->NESTING_LIMIT && !oneIn(3))) {
     if (type.isConcrete()) {
-      if (oneIn(2)) {
+      if (!funcContext || oneIn(2)) {
         return makeConst(type);
       } else {
         return makeLocalGet(type);
       }
     } else if (type == Type::none) {
+      assert(funcContext);
       if (oneIn(2)) {
         return makeNop(type);
       } else {