Fix #27359: Pasting long text crashes blender

Actual problem was caused by insufficient buffer size
in ui_text_leftclip()

Also fixed possible invalid memory write in GHOST_SystemWin32::getClipboard
which was caused by accessing clipboard buffer after closing
clipboard. This mustn't happen.
Also fixed possible crush when buffer was failed to be locked.

source/blender/editors/interface/interface_widgets.c

@@ -888,7 +888,7 @@ static void ui_text_leftclip(uiFontStyle *fstyle, uiBut *but, rcti *rect)
 		/* textbut exception, clip right when... */
 		if(but->editstr && but->pos >= 0) {
 			float width;
-			char buf[256];
+			char buf[UI_MAX_DRAW_STR];
 			
 			/* copy draw string */
 			BLI_strncpy(buf, but->drawstr, sizeof(buf));