patch 8.0.0357: crash when setting 'guicursor' to weird value

Problem:    Crash when setting 'guicursor' to weird value.
Solution:   Avoid negative size. (Dominique Pelle, closes #1465)
diff --git a/src/misc2.c b/src/misc2.c
index 71ca6d8..992e5c2 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -3472,11 +3472,12 @@
 	while (*modep != NUL)
 	{
 	    colonp = vim_strchr(modep, ':');
-	    if (colonp == NULL)
+	    commap = vim_strchr(modep, ',');
+
+	    if (colonp == NULL || (commap != NULL && commap < colonp))
 		return (char_u *)N_("E545: Missing colon");
 	    if (colonp == modep)
 		return (char_u *)N_("E546: Illegal mode");
-	    commap = vim_strchr(modep, ',');
 
 	    /*
 	     * Repeat for all mode's before the colon.
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 11466dc..1ee1f8f 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -235,7 +235,14 @@
   call assert_fails('set statusline=%{', 'E540:')
   call assert_fails('set statusline=' . repeat("%p", 81), 'E541:')
   call assert_fails('set statusline=%(', 'E542:')
-  call assert_fails('set guicursor=x', 'E545:')
+  if has('cursorshape')
+    " This invalid value for 'guicursor' used to cause Vim to crash.
+    call assert_fails('set guicursor=i-ci,r-cr:h', 'E545:')
+    call assert_fails('set guicursor=i-ci', 'E545:')
+    call assert_fails('set guicursor=x', 'E545:')
+    call assert_fails('set guicursor=r-cr:horx', 'E548:')
+    call assert_fails('set guicursor=r-cr:hor0', 'E549:')
+  endif
   call assert_fails('set backupext=~ patchmode=~', 'E589:')
   call assert_fails('set winminheight=10 winheight=9', 'E591:')
   call assert_fails('set winminwidth=10 winwidth=9', 'E592:')
diff --git a/src/version.c b/src/version.c
index 94a325b..2d076cc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    357,
+/**/
     356,
 /**/
     355,