gbproxy: Fix issues found by Coverity

gbproxy_patch_bssgp: Move a check for tlli_info in front of the first
conditional that depends on it, and return immediately if it is NULL.

gbproxy_register_tlli: Initialize tlli_already_known to 0.

Fixes: Coverity CID 1232691
Fixes: Coverity CID 1232692
Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/gb_proxy_tlli.c b/openbsc/src/gprs/gb_proxy_tlli.c
index f554db1..91469b0 100644
--- a/openbsc/src/gprs/gb_proxy_tlli.c
+++ b/openbsc/src/gprs/gb_proxy_tlli.c
@@ -309,7 +309,7 @@
 {
 	struct gbproxy_tlli_info *tlli_info;
 	int enable_patching = -1;
-	int tlli_already_known;
+	int tlli_already_known = 0;
 
 	/* Check, whether the IMSI matches */
 	if (gprs_is_mi_imsi(imsi, imsi_len)) {