softwrap: when switching to another buffer, re-align the starting column

When we switch to another buffer, the window may have been resized
since we were last in this buffer, so make sure that 'firstcolumn'
gets a fitting value.

This fixes https://savannah.gnu.org/bugs/?56991.

Bug existed since version 2.8.0, since the softwrap overhaul.

src/files.c

@@ -610,6 +610,8 @@ void redecorate_after_switch(void)
 	 * turned softwrap mode off while in a different buffer. */
 	if (!ISSET(SOFTWRAP))
 		openfile->firstcolumn = 0;
+	else
+		ensure_firstcolumn_is_aligned();
 #endif
 
 	/* Update titlebar and multiline info to match the current buffer. */