Bug 1561521 - Report error when decoding a value-type and there are no bytes. r=lth

We need to report an error message here or else it will be reported as an OOM.

Differential Revision: https://phabricator.services.mozilla.com/D85070

js/src/wasm/WasmValidate.h

@@ -699,7 +699,7 @@ class Decoder {
     static_assert(uint8_t(TypeCode::Limit) <= UINT8_MAX, "fits");
     uint8_t code;
     if (!readFixedU8(&code)) {
-      return false;
+      return fail("expected type code");
     }
     switch (code) {
       case uint8_t(TypeCode::I32):