When reading PDML files, skip all XML tokens at the start of the file till you reach the first element and then check whether it is 'pdml'

Fixes issue 132

common/pdmlfileformat.cpp

@@ -141,7 +141,14 @@ bool PdmlFileFormat::isMyFileFormat(const QString fileName)
     if (xml.hasError() || !xml.isStartDocument())
         goto _close_exit;
 
-    xml.readNext();
+    // skip everything until the start of the first element
+    while (!xml.isStartElement()) 
+    {
+        xml.readNext();
+        if (xml.hasError())
+            goto _close_exit;
+    }
+
     if (!xml.hasError() && xml.isStartElement() && (xml.name() == "pdml"))
         ret = true;
     else