mpfr: Fix versioning

mingw-w64-mpfr/PKGBUILD

@@ -5,8 +5,11 @@ pkgbase=mingw-w64-${_realname}
 pkgname=("${MINGW_PACKAGE_PREFIX}-${_realname}")
 _pkgver=3.1.4
 _patchlevel=
-pkgver=${_pkgver}.${_patchlevel}
-pkgrel=2
+pkgver=${_pkgver}
+if [ -n "${_patchlevel}" ]; then
+  pkgver+=.${_patchlevel}
+fi
+pkgrel=3
 pkgdesc="Multiple-precision floating-point library (mingw-w64)"
 arch=('any')
 license=('LGPL')