Sync SDL3 wiki -> header

[ci skip]

include/SDL3/SDL_stdinc.h

@@ -2535,8 +2535,8 @@ extern SDL_DECLSPEC Uint32 SDLCALL SDL_StepUTF8(const char **pstr, size_t *pslen
  * This will go to the start of the previous Unicode codepoint in the string,
  * move `*pstr` to that location and return that codepoint.
  *
- * If the resulting codepoint is zero (already at the start of the string), it
- * will not advance `*pstr` at all.
+ * If `*pstr` is already at the start of the string), it will not advance
+ * `*pstr` at all.
  *
  * Generally this function is called in a loop until it returns zero,
  * adjusting its parameter each iteration.