patch 8.1.0073: crash when autocommands call setloclist()

Problem:    Crash when autocommands call setloclist(). (Dominique Pelle)
Solution:   If the quickfix list changes then don't jump to the error.

src/quickfix.c

@@ -6348,9 +6348,11 @@ ex_cexpr(exarg_T *eap)
 	    if (au_name != NULL)
 		apply_autocmds(EVENT_QUICKFIXCMDPOST, au_name,
 						curbuf->b_fname, TRUE, curbuf);
-	    if (res > 0 && (eap->cmdidx == CMD_cexpr ||
+	    if (res > 0 && (eap->cmdidx == CMD_cexpr
-						eap->cmdidx == CMD_lexpr))
+						   || eap->cmdidx == CMD_lexpr)
-		qf_jump(qi, 0, 0, eap->forceit);  /* display first error */
+		    && qi == ll_get_or_alloc_list(curwin))
+		// Jump to the first error if autocmds didn't free the list.
+		qf_jump(qi, 0, 0, eap->forceit);
 	}
 	else
 	    EMSG(_("E777: String or List expected"));

src/testdir/test_quickfix.vim

@@ -3362,3 +3362,14 @@ func Test_lbuffer_with_bwipe()
     au!
   augroup END
 endfunc
+
+func Test_setloclist_in_aucmd()
+  " This was using freed memory.
+  augroup nasty
+    au * * call setloclist(0, [], 'f')
+  augroup END
+  lexpr "x"
+  augroup nasty
+    au!
+  augroup END
+endfunc

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    73,
 /**/
     72,
 /**/