Potential fix #11174, #11175. Use Strnlen

Unsure if this will fix the issue as not reproducable. It is possible
that the pointer passed to this function is bad

src/openrct2/localisation/Localisation.cpp

@@ -370,7 +370,7 @@ static void format_append_string(char** dest, size_t* size, const utf8* string)
 {
     if ((*size) == 0)
         return;
-    size_t length = strlen(string);
+    size_t length = strnlen(string, *size);
     if (length < (*size))
     {
         std::memcpy((*dest), string, length);