range_enc_determine_range(): Don't dereference array on size=0

Change-Id: I5bbb10af8b8e8ebc22bf79f5468e71a41b5e74b3
Fixes: Coverity CID#182710
diff --git a/src/osmo-bsc/arfcn_range_encode.c b/src/osmo-bsc/arfcn_range_encode.c
index 84f9f63..54d98a9 100644
--- a/src/osmo-bsc/arfcn_range_encode.c
+++ b/src/osmo-bsc/arfcn_range_encode.c
@@ -168,6 +168,10 @@
 {
 	int max = 0;
 
+	/* don't dereference arfcns[] array if size is 0 */
+	if (size == 0)
+		return ARFCN_RANGE_128;
+
 	/*
 	 * Go for the easiest. And pick arfcns[0] == f0.
 	 */