Clarify for VS 2013 that an operator bool() method returns bool.

For some reason VS 2013 (unlike its predecessors and other current compilers)
needs us to explicitly convert an operator bool() method's return expression
to bool.  :-P

indra/llcommon/lleventcoro.h

@@ -67,7 +67,7 @@ public:
     LLEventPumpOrPumpName() {}
     operator LLEventPump& () const { return *mPump; }
     LLEventPump& getPump() const { return *mPump; }
-    operator bool() const { return mPump; }
+    operator bool() const { return bool(mPump); }
     bool operator!() const { return ! mPump; }
 
 private: