Fix a few cppcheck issues

Found the following:

* Potential stack explosions with alloca() usage on potentially large
strings
* Memory leaks in WriteEngineServer
* Stack usage out of scope in dataconvert
* A typo in an 'if' statement in dataconvert

writeengine/bulk/we_columninfocompressed.cpp

@@ -411,6 +411,7 @@ int ColumnInfoCompressed::truncateDctnryStore(
             fLog->logMsg( oss.str(), rc, MSGLVL_ERROR );
             fTruncateDctnryFileOp.closeFile( dFile );
 
+            delete [] pointerHdr;
             return rc;
         }