GattServer: Check for null for mServerMap.connIdByAddress

We check for null for mServerMap.connIdByAddress in every places
except in SendResponse and SendNotification. This patch properly
fixes that.

Based on ag/1226721

Bug: 62409644 69965109
Test: Build ok
Change-Id: I104f9d0749af389779ecc33b30e31715b17c21c1
1 file changed