Do not reset the driver registry when the 'load_driver' method of

DriverRegistry is executed second time.

Also, initialize the driver before registering different blueprints,
which uses those driver inside them.

Thanks Khushboo for reporting the issue.

web/pgadmin/__init__.py

@@ -201,6 +201,9 @@ def create_app(app_name=config.APP_NAME):
             from setup import do_upgrade
             do_upgrade(app, user_datastore, security, version)
 
+    # Load all available serve drivers
+    driver.init_app(app)
+
     ##########################################################################
     # Load plugin modules
     ##########################################################################
@@ -252,9 +255,6 @@ def create_app(app_name=config.APP_NAME):
             'current_blueprint': current_blueprint
             }
 
-    # Load all available serve drivers
-    driver.init_app(app)
-
     ##########################################################################
     # All done!
     ##########################################################################

web/pgadmin/utils/driver/registry.py

@@ -46,7 +46,7 @@ class DriverRegistry(ABCMeta):
       - Use this function from init_app(...) to load all available drivers in
         the registry.
     """
-    registry = dict()
+    registry = None
     drivers = dict()
 
     def __init__(cls, name, bases, d):
@@ -76,6 +76,8 @@ class DriverRegistry(ABCMeta):
 
     @classmethod
     def load_drivers(cls):
+        # Initialize the registry only if it has not yet been initialized
+        if DriverRegistry.registry is None:
             DriverRegistry.registry = dict()
 
         from importlib import import_module