Return appropiate value in xbps_check_is_installed_pkg().

Return -1 if package is not installed or dependency not satisfied.
Return 0 if same version required is already installed.
Return 1 if installed version is greater than required.

--HG--
extra : convert_revision : 359b79cbe809e1818fe999dc1d55da7e635dbe44

lib/util.c

@@ -125,7 +125,7 @@ xbps_check_is_installed_pkg(const char *pkg)
 	dict = xbps_find_pkg_installed_from_plist(pkgname);
 	if (dict == NULL) {
 		free(pkgname);
-		return 1; /* not installed */
+		return -1; /* not installed */
 	}
 
 	/* Get version from installed package */