core: Log any exception during panic because of exception

panic() calls a good amount of code, so it could get another exception.
The SynchronizationContext is running on an arbitrary thread and we
don't want to propagate this secondary exception up its stack (to be
handled by its UncaughtExceptionHandler); it we wanted that we'd
propagate the original exception.

This second exception will only be seen in the logs; the first exception
was logged and will be used to fail RPCs.

Also related to http://yaqs/8493785598685872128 and b692b9d

Author: ejona86

core/src/main/java/io/grpc/internal/ManagedChannelImpl.java

@@ -187,7 +187,12 @@ public void uncaughtException(Thread t, Throwable e) {
               Level.SEVERE,
               "[" + getLogId() + "] Uncaught exception in the SynchronizationContext. Panic!",
               e);
-          panic(e);
+          try {
+            panic(e);
+          } catch (Throwable anotherT) {
+            logger.log(
+                Level.SEVERE, "[" + getLogId() + "] Uncaught exception while panicking", anotherT);
+          }
         }
       });