BUG/MINOR: sample: free err2 in smp_resolve_args for type ARGT_REG

The err2 may be leaking memory in case an error occurred as a result of
regex_comp() call.

src/sample.c

@@ -1638,6 +1638,7 @@ int smp_resolve_args(struct proxy *p, char **err)
 					  *err ? *err : "", cur->file, cur->line,
 					 arg->data.str.area,
 					 cur->arg_pos + 1, conv_pre, conv_ctx, conv_pos, ctx, cur->kw, where, p->id, err2);
+				ha_free(&err2);
 				cfgerr++;
 				continue;
 			}