build: add install_files call after the mpv target was defined

This makes it work on cold compiles when there is no `build/` directory and
one does ./waf configure && ./waf install (i.e.: no ./waf build).

wscript_build.py

@@ -419,8 +419,6 @@ def build(ctx):
         resources       = [node.srcpath() for node in resources_nodes]
         cprog_kwargs['mac_resources'] = resources
 
-        ctx.install_files(ctx.env.BINDIR, 'mpv')
-
     ctx(
         target       = "mpv",
         source       = ctx.filtered_sources(sources),
@@ -432,6 +430,9 @@ def build(ctx):
         **cprog_kwargs
     )
 
+    if ctx.dependency_satisfied('macosx-bundle'):
+        ctx.install_files(ctx.env.BINDIR, 'mpv')
+
     if ctx.dependency_satisfied("vf-dlopen-filters"):
         dlfilters = "showqscale telecine tile rectangle framestep \
                      ildetect".split()