msm: ipa3: add check on qmi-client handler

In some cases with IPA3 received qmi_service_exit from
modem but still uses invalid qmi-handler to send QMI-msg
to modem which leads to crash. The fix is to add the
check before sending QMI msg to modem.

Change-Id: Iac48747a188b234cc640285e181984985fc3c012
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>