noh_string_replace: Use arena from source string

src/noh.h

@@ -381,6 +381,8 @@ void noh_string_append_cstr(Noh_String *string, const char *cstr);
 void noh_string_append_null(Noh_String *string);
 
 // Replace all occurrences of one character with another in a Noh_String.
+// If the string does not use an arena, its original data will be cleared.
+// If it does not use an arena, this data will remain orphaned in the arena.
 void noh_string_replace(Noh_String *string, const char from, const char to);
 
 // Frees a Noh_String, freeing the memory used and settings the count and capacity to 0.
@@ -922,6 +924,7 @@ void noh_string_append_null(Noh_String *string) {
 
 void noh_string_replace(Noh_String *string, const char from, const char to) {
     Noh_String result = {0};
+    result.arena = string->arena;
     for (size_t i = 0; i < string->count; i++) {
         if (result.arena) {
             if (string->elems[i] == from) {