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)

Author: brammool

runtime/doc/eval.txt

@@ -1,4 +1,4 @@
-*eval.txt*	For Vim version 8.0.  Last change: 2017 Dec 16
+*eval.txt*	For Vim version 8.0.  Last change: 2017 Dec 19
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -3338,8 +3338,8 @@ count({comp}, {expr} [, {ic} [, {start}]])			*count()*
 		When {ic} is given and it's |TRUE| then case is ignored.
 
 		When {comp} is a string then the number of not overlapping
-		occurrences of {expr} is returned.
-
+		occurrences of {expr} is returned. Zero is returned when
+		{expr} is an empty string.
 
 							*cscope_connection()*
 cscope_connection([{num} , {dbpath} [, {prepend}]])

src/evalfunc.c

@@ -2382,7 +2382,7 @@ f_count(typval_T *argvars, typval_T *rettv)
 	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)
 	    {

src/testdir/test_functions.vim

@@ -692,6 +692,7 @@ func Test_count()
   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()

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1410,
 /**/
     1409,
 /**/