eeschema: Disabled an assert checking if project path is empty

Empty project path is a valid case when eeschema is executed in
standalone mode without any file loaded.

There were no observed harmful consequences of running eeschema without
the project path set, but to stay safe the project specific
sym-lib-table load code is executed only when the project path is set.

eeschema/eeschema_config.cpp

@@ -779,8 +779,8 @@ SYMBOL_LIB_TABLE* PROJECT::SchSymbolLibTable()
 
         wxGetEnv( PROJECT_VAR_NAME, &prjPath );
 
-        wxASSERT( !prjPath.empty() );
-
+        if( !prjPath.IsEmpty() )
+        {
             wxFileName fn( prjPath, SYMBOL_LIB_TABLE::GetSymbolLibTableFileName() );
 
             try
@@ -795,6 +795,7 @@ SYMBOL_LIB_TABLE* PROJECT::SchSymbolLibTable()
                 DisplayErrorMessage( NULL, msg, ioe.What() );
             }
         }
+    }
 
     return tbl;
 }