PoW Worker should wait for sql thread to init

- I think this was causing freezing queue on launch if not empty
- I can't reproduce the bug anymore

src/class_singleWorker.py

@@ -52,6 +52,11 @@ class singleWorker(threading.Thread, StoppableThread):
 
     def run(self):
 
+        while not state.sqlReady and state.shutdown == 0:
+            self.stop.wait(2)
+        if state.shutdown > 0:
+            return
+        
         # Initialize the neededPubkeys dictionary.
         queryreturn = sqlQuery(
             '''SELECT DISTINCT toaddress FROM sent WHERE (status='awaitingpubkey' AND folder='sent')''')

src/class_sqlThread.py

@@ -494,6 +494,8 @@ class sqlThread(threading.Thread):
                 parameters = (int(time.time()),)
                 self.cur.execute(item, parameters)
 
+        state.sqlReady = True
+
         while True:
             item = helper_sql.sqlSubmitQueue.get()
             if item == 'commit':

src/state.py

@@ -19,6 +19,8 @@ shutdown = 0 #Set to 1 by the doCleanShutdown function. Used to tell the proof o
 
 curses = False
 
+sqlReady = False # set to true by sqlTread when ready for processing
+
 # If the trustedpeer option is specified in keys.dat then this will
 # contain a Peer which will be connected to instead of using the
 # addresses advertised by other peers. The client will only connect to