make config optional when using common.set_FDroidPopen_env()

common.set_FDroidPopen_env() is used to call git and other tools that
are not part of the Android SDK nor require Java, so the items that
are being set from the config are optional.  This lets plugins do
quite a bit without ever setting up a config.

examples/fdroid_fetchsrclibs.py

@@ -14,10 +14,6 @@ fdroid_summary = 'prepare the srclibs for `fdroid build --on-server`'
 
 
 def main():
-    common.config = {
-        'sdk_path': os.getenv('ANDROID_HOME'),
-    }
-    common.fill_config_defaults(common.config)
     parser = argparse.ArgumentParser(usage="%(prog)s [options] [APPID[:VERCODE] [APPID[:VERCODE] ...]]")
     common.setup_global_opts(parser)
     parser.add_argument("appid", nargs='*', help=_("applicationId with optional versionCode in the form APPID[:VERCODE]"))

fdroidserver/common.py

@@ -2741,10 +2741,12 @@ def set_FDroidPopen_env(build=None):
     if env is None:
         env = os.environ
         orig_path = env['PATH']
-        for n in ['ANDROID_HOME', 'ANDROID_SDK']:
-            env[n] = config['sdk_path']
-        for k, v in config['java_paths'].items():
-            env['JAVA%s_HOME' % k] = v
+        if config:
+            if config.get('sdk_path'):
+                for n in ['ANDROID_HOME', 'ANDROID_SDK']:
+                    env[n] = config['sdk_path']
+            for k, v in config.get('java_paths', {}).items():
+                env['JAVA%s_HOME' % k] = v
 
     missinglocale = True
     for k, v in env.items():