VBOX: Check for a valid Console pointer before attempting to pause/resume the VM.

get_Console() is not returning an error, bit the returning IConsole interface is NULL.  Just return an ERR_EXEC instead of crash.

samples/vboxwrapper/vbox_mscom_impl.cpp

@@ -1516,10 +1516,12 @@ int VBOX_VM::pause() {
     if (CHECK_ERROR(rc)) goto CLEANUP;
 
     // Pause the machine.
+    if (pConsole) {
         rc = pConsole->Pause();
         if (CHECK_ERROR(rc)) goto CLEANUP;
 
         retval = BOINC_SUCCESS;
+    }
 
 CLEANUP:
     return retval;
@@ -1543,10 +1545,12 @@ int VBOX_VM::resume() {
     if (CHECK_ERROR(rc)) goto CLEANUP;
 
     // Resume the machine.
+    if (pConsole) {
         rc = pConsole->Resume();
         if (CHECK_ERROR(rc)) goto CLEANUP;
 
         retval = BOINC_SUCCESS;
+    }
 
 CLEANUP:
     return retval;