CLEANUP: pattern: Ignore unknown samples in pat_match_ip().

Ignore samples that are neither SMP_T_IPV4 nor SMP_T_IPV6 instead of
matching with an uninitialized value in this case.

This situation should not occur in the current codebase but triggers
warnings in static code analysis tools.

Found in haproxy 1.5.

src/pattern.c

@@ -1021,6 +1021,9 @@ struct pattern *pat_match_ip(struct sample *smp, struct pattern_expr *expr, int
 			}
 			else
 				continue;
+		} else {
+		  /* impossible */
+		  continue;
 		}
 
 		/* Check if the input sample match the current pattern. */