Revert "exec: prevent a command in a current dirctory from being executed"

This reverts commit 1b4d572b77.

An empty path is treated as a current directory in Unix, too.

exec.c

@@ -1332,15 +1332,6 @@ search_path(const char *name, const char *lpath,
 		sp = p;
 		XcheckN(xs, xp, namelen);
 		memcpy(xp, name, namelen);
-#ifdef __OS2__
-		/*
-		 * Skip path without a directory part to prevent from searching the
-		 * current directory. For example, PATH=;...;;...;
-		 */
-		if (!mksh_vdirsep(Xstring(xs, xp)))
-		/* nothing */;
-		else
-#endif
 		if ((ev = search_access(Xstring(xs, xp), mode)) == 0) {
 			name = Xclose(xs, xp + namelen);
 			goto search_path_ok;