cutting: do nothing when trying to chop a word leftward at start of file

Instead of marking the buffer as modified, provide the feedback that
"nothing was cut", like when trying to chop a word rightward at the
end of the buffer.

This fixes https://savannah.gnu.org/bugs/?57015.

Bug existed since version 4.4, commit 4314b8de.

src/cut.c

@@ -194,7 +194,10 @@ void chop_word(bool forward)
 /* Delete a word leftward. */
 void chop_previous_word(void)
 {
-	chop_word(BACKWARD);
+	if (openfile->current->prev == NULL && openfile->current_x == 0)
+		statusbar(_("Nothing was cut"));
+	else
+		chop_word(BACKWARD);
 }
 
 /* Delete a word rightward. */