Update gps_client.py return -1 if no socket

gps_client.py

@@ -11,18 +11,17 @@ run this way: python3 example1.py.txt
 import gps               # the gpsd interface module
 import time
 
-session = gps.gps(mode=gps.WATCH_ENABLE)
-
-start = time.perf_counter()
-
 mode = -1    
-
 lat = 0    
-
 lon = 0    
-
 alt = 0
 
+try:
+    
+    session = gps.gps(mode=gps.WATCH_ENABLE)
+    
+    start = time.perf_counter()
+    
     try:
         while (session.read() == 0) and ((time.perf_counter() - start) < 2) and (mode < 2):
     #        print(gps.MODE_SET)