Add missing unlock(s) in dahdi_read

(two cases in trunk)

(closes issue #15683)
Reported by: alecdavis



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@222462 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_dahdi.c

@@ -5081,7 +5081,10 @@ static struct ast_frame  *dahdi_read(struct ast_channel *ast)
 		return NULL;
 	}
 	
-	if ((p->radio || (p->oprmode < 0)) && p->inalarm) return NULL;
+	if ((p->radio || (p->oprmode < 0)) && p->inalarm) {
+		ast_mutex_unlock(&p->lock);
+		return NULL;
+	}
 
 	p->subs[index].f.frametype = AST_FRAME_NULL;
 	p->subs[index].f.datalen = 0;