meson: wildmidi detection fixes

Need at least 0.4.2 apparently.

ext/wildmidi/meson.build:11:2: ERROR:  String '' cannot be converted to int
6 jobs for meson-wildmidi-detection-fixes in 26 minutes and 18 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #65754
gst indent

00:00:28

passed #65753
manifest

00:00:19

 
  Build
passed #65755
build fedora x86_64

00:02:57

 
  Test
passed #65756
check fedora

00:15:48

 
  Full Builds
passed #65757
build android arm64 api28

00:03:02

passed #65758
build cerbero fedora x86_64

00:05:37