stb_textedit: fix find_charpos for n == z to make cursor move correct…

…ly when pressing up

stb_textedit.h

@@ -518,39 +518,17 @@ static void stb_textedit_find_charpos(StbFindState *find, STB_TEXTEDIT_STRING *s
    int z = STB_TEXTEDIT_STRINGLEN(str);
    int i=0, first;
 
-   if (n == z) {
-      // if it's at the end, then find the last line -- simpler than trying to
-      // explicitly handle this case in the regular code
-      if (single_line) {
-         STB_TEXTEDIT_LAYOUTROW(&r, str, 0);
-         find->y = 0;
-         find->first_char = 0;
-         find->length = z;
-         find->height = r.ymax - r.ymin;
-         find->x = r.x1;
-      } else {
-         find->y = 0;
-         find->x = 0;
-         find->height = 1;
-         while (i < z) {
-            STB_TEXTEDIT_LAYOUTROW(&r, str, i);
-            prev_start = i;
-            i += r.num_chars;
-         }
-         find->first_char = i;
-         find->length = 0;
-         find->prev_first = prev_start;
-      }
-      return;
-   }
-
    // search rows to find the one that straddles character n
    find->y = 0;
 
    for(;;) {
       STB_TEXTEDIT_LAYOUTROW(&r, str, i);
-      if (n < i + r.num_chars)
-         break;
+      // this is an optimization to avoid checking n == z in every iteration
+      if (n <= i + r.num_chars) {
+         if (n < i + r.num_chars || n == z) {
+            break;
+         }
+      }
       prev_start = i;
       i += r.num_chars;
       find->y += r.baseline_y_delta;