scons: remove file existence check from InstallData

It was breaking install of generated files. Also adjusted manpage
install which was relying on this behavior.
This helps with issue wesnoth#5692

SConstruct

@@ -738,8 +738,9 @@ linguas = Split(File("po/LINGUAS").get_contents().decode("utf-8"))
 def InstallManpages(env, component):
     env.InstallData("mandir", component, os.path.join("doc", "man", component + ".6"), "man6")
     for lingua in linguas:
-        manpage = os.path.join("doc", "man", lingua, component + ".6")
-        env.InstallData("mandir", component, manpage, os.path.join(lingua, "man6"))
+        manpage = FindFile(os.path.join(lingua, component + ".6"), "doc/man")
+        if manpage:
+            env.InstallData("mandir", component, manpage, os.path.join(lingua, "man6"))
 
 # Now the actual installation productions
 

scons/install.py

@@ -73,8 +73,7 @@ def InstallData(env, datadir, component, source, subdir = "", **kwargs):
         if isinstance(source, SCons.Node.FS.Dir) or source.isdir():
             dirs.append(source)
         else:
-            if source.exists():
-                env.Alias("install-" + component, env.Install(installdir, source, **kwargs))
+            env.Alias("install-" + component, env.Install(installdir, source, **kwargs))
     if dirs:
         if len(dirs) == 1:
             install = env.InstallFiltered(installdir.path, dirs[0].path, **kwargs)