patch 8.0.1410: hang when using count() with an empty string

Problem:    Hang when using count() with an empty string.
Solution:   Return zero for an empty string. (Dominique Pelle, closes #2465)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 9aacd30..7f78a9d 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2382,7 +2382,7 @@
 	char_u *p = argvars[0].vval.v_string;
 	char_u *next;
 
-	if (!error && expr != NULL && p != NULL)
+	if (!error && expr != NULL && *expr != NUL && p != NULL)
 	{
 	    if (ic)
 	    {
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index d904013..20e4280 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -692,6 +692,7 @@
   call assert_equal(0, count("foo", "O"))
   call assert_equal(2, count("foo", "O", 1))
   call assert_equal(2, count("fooooo", "oo"))
+  call assert_equal(0, count("foo", ""))
 endfunc
 
 func Test_changenr()
diff --git a/src/version.c b/src/version.c
index 97f0d66..cf53357 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1410,
+/**/
     1409,
 /**/
     1408,