fix(string): avoid empty-pattern loop (#141)

An empty search pattern never advances either strstr loop. Treat it as a successful no-op, matching the existing no-match behavior.

Confidence: high

Scope-risk: narrow

Tested: official sc_str CMake test with ASan; GCC 13 ASan/UBSan; MinGW GCC 8

Not-tested: MSVC

Author: 94xhn

string/sc_str.c

@@ -367,6 +367,10 @@ bool sc_str_replace(char **str, const char *replace, const char *with)
 	rep_len = strlen(replace);
 	with_len = strlen(with);
 
+	if (rep_len == 0) {
+		return true;
+	}
+
 	if (rep_len >= UINT32_MAX || with_len >= UINT32_MAX) {
 		return false;
 	}

string/str_test.c

@@ -459,6 +459,11 @@ void test5(void)
 	assert(strcmp(s1, "longeRlongeR") == 0);
 	assert(sc_str_replace(&s1, "longeR", ""));
 	assert(strcmp(s1, "") == 0);
+	sc_str_set(&s1, "unchanged");
+	assert(sc_str_replace(&s1, "", "x"));
+	assert(strcmp(s1, "unchanged") == 0);
+	assert(sc_str_replace(&s1, "", ""));
+	assert(strcmp(s1, "unchanged") == 0);
 	sc_str_destroy(&s1);
 
 	s1 = sc_str_create("*test * test*");