Mark a Python plugin without an __init__.py as broken

utils.findPlugins() checks for the existence of an __init__.py which
results in an attempt to enable a plugin without an __init__.py being
blocked with the only notification being a message in the Plugins log:

WARNING    Plugin "<name>" is not compatible with this version of QGIS.
             It will be disabled.

This is not very informative, especially because it is the same message
used for a metadata version mismatch.

Adding this check to Plugins.getInstalledPlugin(), which already
duplicates the metadata checks from utils.findPlugins(), results in the
plugin being marked as broken in the Plugins dialog.

Author: cjmayo

python/pyplugin_installer/installer_data.py

@@ -600,6 +600,10 @@ def pluginMetadata(fct):
         errorDetails = ""
         version = None
 
+        if not os.path.exists(os.path.join(path, '__init__.py')):
+            error = "broken"
+            errorDetails = QCoreApplication.translate("QgsPluginInstaller", "Missing __init__.py")
+
         metadataFile = os.path.join(path, 'metadata.txt')
         if os.path.exists(metadataFile):
             version = normalizeVersion(pluginMetadata("version"))