patch 8.1.1740: exepath() doesn't work for "bin/cat"

Problem:    Exepath() doesn't work for "bin/cat".
Solution:   Check for any path separator. (Daniel Hahler, closes #4724,
            closes #4710)
diff --git a/src/os_unix.c b/src/os_unix.c
index a15d660..6387a77 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3103,12 +3103,11 @@
 
     /* When "use_path" is false and if it's an absolute or relative path don't
      * need to use $PATH. */
-    if (!use_path || mch_isFullName(name) || (name[0] == '.'
-		   && (name[1] == '/' || (name[1] == '.' && name[2] == '/'))))
+    if (!use_path || gettail(name) != name)
     {
 	/* There must be a path separator, files in the current directory
 	 * can't be executed. */
-	if (gettail(name) != name && executable_file(name))
+	if ((use_path || gettail(name) != name) && executable_file(name))
 	{
 	    if (path != NULL)
 	    {