tty: vt: initialize softcursor_original correctly

add_softcursor() stores the contents of the text buffer position in this variable before drawing the softcursor, whereas hide_softcursor() writes the value back. A value of -1 means that no cursor has been drawn and therefore no character is to be restored. softcursor_original, however, is only implicitly initialized with 0. Therefore, when hide_softcursor is called for the first time (console_init -> con_init -> redraw_screen -> hide_cursor), it wrongly writes 0x0000 in the top left corner of the text buffer. Normally, this is just as black as the rest of the screen (vc_video_erase_char) and can't be seen, but it appears as a black cursor rectangle on non-black backgrounds e.g. with boot option "vt.global_cursor_default=0 vt.color=0xf0". softcursor_original needs to be initialized with -1.

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index 4462d16..8ea3543 100644
@@ -568,7 +568,7 @@ static void delete_char(struct vc_data *vc, unsigned int nr)
 			vc->vc_cols - vc->vc_x);
 }
 
-static int softcursor_original;
+static int softcursor_original = -1;
 
 static void add_softcursor(struct vc_data *vc)
 {