[wasm][fuzzer] Check that global init. does not start beyond code end

Bug: chromium:1104053
Change-Id: Iacfeeb80ab981f20dc2fc40cf8435514876fcf28
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2307233Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68944}

src/wasm/module-decoder.cc

@@ -1638,6 +1638,10 @@ class ModuleDecoderImpl : public Decoder {
   }
 
   WasmInitExpr consume_init_expr(WasmModule* module, ValueType expected) {
+    if (pc() >= end()) {
+      error(pc(), "Global initializer starting beyond code end");
+      return {};
+    }
     constexpr Decoder::ValidateFlag validate = Decoder::kValidate;
     WasmOpcode opcode = kExprNop;
     std::vector<WasmInitExpr> stack;