patch 8.2.0896: crash when calling searchcount() with a string

Problem:    Crash when calling searchcount() with a string.
Solution:   Check the argument is a dict. (closes #6192)
diff --git a/src/testdir/test_search_stat.vim b/src/testdir/test_search_stat.vim
index 668545c..85e4f86 100644
--- a/src/testdir/test_search_stat.vim
+++ b/src/testdir/test_search_stat.vim
@@ -259,6 +259,10 @@
   bwipe!
 endfunc
 
+func Test_searchcount_fails()
+  call assert_fails('echo searchcount("boo!")', 'E715:')
+endfunc
+
 func Test_search_stat_foldopen()
   CheckScreendump