Don't bother re-encoding Latin1 characters in the ASCII range

(cherry picked from commit 6150b5b3cbde0e592c4ffe822f66aa5f9c90c3d9)

src/SDL_utils_c.h

@@ -27,9 +27,6 @@
 /* Return the smallest power of 2 greater than or equal to 'x' */
 extern int SDL_powerof2(int x);
 
-/* Return whether the string is valid UTF8 */
-extern SDL_bool SDL_utf8valid(const char *str, size_t bytes);
-
 #endif /* SDL_utils_h_ */
 
 /* vi: set ts=4 sw=4 expandtab: */

src/stdlib/SDL_string.c

@@ -621,42 +621,6 @@ SDL_utf8strnlen(const char *str, size_t bytes)
     return retval;
 }
 
-SDL_bool SDL_utf8valid(const char *str, size_t bytes)
-{
-    while (*str && bytes > 0) {
-        Uint8 ch = (Uint8)*str;
-
-        if (ch <= 0x7F) {
-            ++str;
-            --bytes;
-            continue;
-        }
-
-        if (UTF8_IsLeadByte(ch)) {
-            size_t left = UTF8_TrailingBytes(ch);
-            if (bytes < left) {
-                return SDL_FALSE;
-            }
-
-            ++str;
-            --bytes;
-
-            while (left-- > 0) {
-                ch = (Uint8)*str;
-                if (!UTF8_IsTrailingByte(ch)) {
-                    return SDL_FALSE;
-                }
-
-                ++str;
-                --bytes;
-            }
-        } else {
-            return SDL_FALSE;
-        }
-    }
-    return SDL_TRUE;
-}
-
 size_t
 SDL_strlcat(SDL_INOUT_Z_CAP(maxlen) char *dst, const char *src, size_t maxlen)
 {

src/video/x11/SDL_x11events.c

@@ -740,10 +740,22 @@ static Bool isReparentNotify(Display *display, XEvent *ev, XPointer arg)
            ev->xreparent.serial == unmap->serial;
 }
 
+static SDL_bool IsHighLatin1(const char *string, int length)
+{
+	while (length-- > 0) {
+		Uint8 ch = (Uint8)*string;
+		if (ch >= 0x80) {
+			return SDL_TRUE;
+		}
+		++string;
+	}
+	return SDL_FALSE;
+}
+
 static int XLookupStringAsUTF8(XKeyEvent *event_struct, char *buffer_return, int bytes_buffer, KeySym *keysym_return, XComposeStatus *status_in_out)
 {
     int result = X11_XLookupString(event_struct, buffer_return, bytes_buffer, keysym_return, status_in_out);
-    if (result > 0 && !SDL_utf8valid(buffer_return, (size_t)result)) {
+    if (IsHighLatin1(buffer_return, result)) {
         char *utf8_text = SDL_iconv_string("UTF-8", "ISO-8859-1", buffer_return, result);
         if (utf8_text) {
             SDL_strlcpy(buffer_return, utf8_text, bytes_buffer);