Handle missing opId gracefully

[bartlomieju]

This has been coming up several times already; I need to finally fix it. The problem is that we use unwrap when trying to cast opId to Uint32 - this panics if opId is undefined. Such situation should be handled gracefully by returning error to JS or adding assert on opId in Deno.core.dispatch - whichever will have smaller impact on performace.

https://github.com/denoland/deno/pull/4118/checks?check_run_id=466535527

##[error]thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: TryFromTypeError { expected_type: "Uint32" }', src/libcore/result.rs:1188:5
stack backtrace:
   0:        0x104176eb5 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h109831b4e69a3cdc
   1:        0x10419e4d0 - core::fmt::write::haefb4093ced4abcf
   2:        0x10417089b - std::io::Write::write_fmt::h32eef7193f012831
   3:        0x104179393 - std::panicking::default_hook::{{closure}}::hd11104060d683e7f
   4:        0x10417909a - std::panicking::default_hook::h3ac89e0bbec67847
   5:        0x104179a3b - std::panicking::rust_panic_with_hook::h497844b5b7d1708e
   6:        0x1041795d9 - rust_begin_unwind
   7:        0x1041bf4ec - core::panicking::panic_fmt::h2877d31f4cece04d
   8:        0x1041bf5c9 - core::result::unwrap_failed::h41045cf6a251332f
   9:        0x1036a1ddf - deno_core::bindings::send::h47170700ae11a5f0
  10:        0x1036b9e6d - <extern "C" fn(A0) .> R as rusty_v8::support::CFnFrom<F>>::mapping::c_fn::h1852c76360317199
  11:        0x10372af03 - _ZN2v88internal25FunctionCallbackArguments4CallENS0_15CallHandlerInfoE
  12:        0x10372a37d - _ZN2v88internal12_GLOBAL__N_119HandleApiCallHelperILb0EEENS0_11MaybeHandleINS0_6ObjectEEEPNS0_7IsolateENS0_6HandleINS0_10HeapObjectEEESA_NS8_INS0_20FunctionTemplateInfoEEENS8_IS4_EENS0_16BuiltinArgumentsE
  13:        0x103729911 - _ZN2v88internalL26Builtin_Impl_HandleApiCallENS0_16BuiltinArgumentsEPNS0_7IsolateE
fatal runtime error: failed to initiate panic, error 5

CC @ry