In rigctld do not try to close fsockin/fsockout when null -- happens during error on fsockin or fsockout

https://github.com/Hamlib/Hamlib/issues/757

Segfault-award

@@ -22,3 +22,6 @@ Here is the list of the brave fellows:
 * Charles Suprin AA1VS, v1.2.12, 02/2011, all user programs/daemons
     $ rigctl -C MGP
 
+* Chuck Ritola
+    fclose of fsockin or fsockout when null 
+    https://github.com/Hamlib/Hamlib/issues/757

tests/rigctld.c

@@ -1221,8 +1221,8 @@ handle_exit:
     if (retcode != 0) { rig_debug(RIG_DEBUG_ERR, "%s: fclose(fsockin) %s\n", __func__, strerror(retcode)); }
 
 #endif
-    fclose(fsockin);
-    fclose(fsockout);
+    if (fsockin) fclose(fsockin);
+    if (fsockout) fclose(fsockout);
 
 // for everybody else we close the handle after fclose
 #ifndef __MINGW32__