ci/win32: add zlib

It should work out of the box, but upstream meson wrap is not robust in
this case.

ci/build-win32.ps1

@@ -69,11 +69,19 @@ git clone https://github.com/arch1t3cht/Aegisub --depth 1
 Copy-Item -Path "Aegisub/subprojects/packagefiles/luajit/*" `
           -Destination "$subprojects/packagefiles/luajit" -Recurse -Force
 
+# Patch for ffmpeg wrap to allow internal meson dependencies (needed for zlib)
+if (-not (Test-Path "$subprojects/packagefiles/ffmpeg")) {
+    New-Item -Path "$subprojects/packagefiles/ffmpeg" -ItemType Directory | Out-Null
+}
+Copy-Item -Path "Aegisub/subprojects/packagefiles/ffmpeg/0001.patch" `
+          -Destination "$subprojects/packagefiles/ffmpeg" -Force
+
 $projects = @(
     @{
         Path = "$subprojects/ffmpeg.wrap"
         URL = "https://gitlab.freedesktop.org/gstreamer/meson-ports/ffmpeg.git"
         Revision = "meson-6.1"
+        Patch = "ffmpeg/0001.patch"
         Provides = @(
             "libavcodec = libavcodec_dep",
             "libavdevice = libavdevice_dep",
@@ -134,6 +142,9 @@ clone-recursive = true
     if ($project.ContainsKey('PatchDir')) {
         $content += "`npatch_directory = $($project.PatchDir)"
     }
+    if ($project.ContainsKey('Patch')) {
+        $content += "`ndiff_files = $($project.Patch)"
+    }
     if ($project.ContainsKey('Provides')) {
         $provide = "[provide]`n$($project.Provides -join "`n")"
         $content += "`n$provide"
@@ -142,6 +153,7 @@ clone-recursive = true
 }
 
 meson setup build `
+    --force-fallback-for=zlib `
     -Ddefault_library=static `
     -Dlibmpv=true `
     -Dtests=true `