Fix realloc(3) error handling

From realloc(3) manpage:
       The realloc() function returns a pointer to the newly allocated memory,
       which  is  suitably  aligned for any built-in type and may be different
       from ptr, or NULL if the request fails.  If size was equal to 0, either
       NULL  or  a  pointer  suitable  to be passed to free() is returned.  If
       realloc() fails, the original block is left untouched; it is not  freed
       or moved.

If realloc() fails then the memory that was previously allocated needs
to be freed, or it will create a memory leak.

It was not a real problem because if realloc(3) failed then pcscd would
exit immediatly and the memory would not leak for a long time.

Thanks to PA193 project
https://github.com/vegaMato/PCSC-lite-project-tasks

src/hotplug_libudev.c

@@ -228,15 +228,19 @@ static LONG HPReadBundleValues(void)
 					Log2(PCSC_LOG_INFO,
 						"Increase driverTracker to %d entries", driverSize);
 #endif
-					driverTracker = realloc(driverTracker,
+
+					void* tmp = realloc(driverTracker,
 						driverSize * sizeof(*driverTracker));
-					if (NULL == driverTracker)
+
+					if (NULL == tmp)
 					{
+						free(driverTracker);
 						Log1(PCSC_LOG_CRITICAL, "Not enough memory");
 						driverSize = -1;
 						(void)closedir(hpDir);
 						return -1;
 					}
+					driverTracker = tmp;
 
 					/* clean the newly allocated entries */
 					for (i=driverSize-DRIVER_TRACKER_SIZE_STEP; i<driverSize; i++)

src/hotplug_libusb.c

@@ -234,15 +234,17 @@ static LONG HPReadBundleValues(void)
 					Log2(PCSC_LOG_INFO,
 						"Increase driverTracker to %d entries", driverSize);
 #endif
-					driverTracker = realloc(driverTracker,
+					void* tmp = realloc(driverTracker,
 						driverSize * sizeof(*driverTracker));
-					if (NULL == driverTracker)
+					if (NULL == tmp)
 					{
+						free(driverTracker);
 						Log1(PCSC_LOG_CRITICAL, "Not enough memory");
 						driverSize = -1;
 						closedir(hpDir);
 						return -1;
 					}
+					driverTracker = tmp;
 
 					/* clean the newly allocated entries */
 					for (i=driverSize-DRIVER_TRACKER_SIZE_STEP; i<driverSize; i++)