Have a DelegateCall error not abort the runtime (#360)

Summary:
Pull Request resolved: #360

Right now if a DelegateCall returns an Error it causes the whole runtime to crash.
This causes stuff in python unit tests to crash all of the tests at once without an
exception.

Change it to return the Error code instead of using `ET_CHECK`

Differential Revision: D49321324

fbshipit-source-id: cac73016366417f708d940d8fc46e069a19640e1

Author: dulinriley

runtime/executor/method.cpp

@@ -948,11 +948,14 @@ Error Method::execute_instruction() {
       Error err = delegates_[delegate_idx].Execute(
           backend_execution_context,
           chain.argument_lists_[step_state_.instr_idx].data());
-      ET_CHECK_MSG(
-          err == Error::Ok,
-          "CALL_DELEGATE execute failed at instruction %zu: %" PRIu32,
-          step_state_.instr_idx,
-          err);
+      if (err != Error::Ok) {
+        ET_LOG(
+            Error,
+            "CALL_DELEGATE execute failed at instruction %zu: %" PRIu32,
+            step_state_.instr_idx,
+            err);
+        return err;
+      }
     } break;
     case executorch_flatbuffer::InstructionArguments::JumpFalseCall: {
       EXECUTORCH_SCOPE_PROF("JF_CALL");