Fuzzer: Fix Merge fuzzing when input must be ignored (WebAssembly#7866)

I saw a failure where the second module hit a VM limit, so it should be
ignored, but we weren't, and ended up thinking it behaved differently
after merge.

Author: kripken

scripts/fuzz_opt.py

@@ -1485,11 +1485,17 @@ def handle(self, wasm):
 
         # verify that merging in the second module did not alter the output.
         output = run_bynterp(wasm, ['--fuzz-exec-before', '-all'])
+        if output == IGNORE:
+            return
         output = fix_output(output)
         second_output = run_bynterp(second_wasm, ['--fuzz-exec-before', '-all'])
         second_output = fix_output(second_output)
+        if second_output == IGNORE:
+            return
         merged_output = run_bynterp(merged, ['--fuzz-exec-before', '-all'])
         merged_output = fix_output(merged_output)
+        if merged_output == IGNORE:
+            return
 
         # If the second module traps in instantiation, then the merged module
         # must do so as well, regardless of what the first module does. (In