PFW: Prevent crash if subsystem structure missing

BZ: 62524

If the XML file defining a subsystem is missing, the PFW crashes
without any message.
This patch fixes this issue.

Change-Id: Ibc0e9d195a8207d41d25613f56d1c9740bf6c784
Signed-off-by: Frédéric Boisnard <fredericx.boisnard@intel.com>
Reviewed-on: http://android.intel.com:8080/70698
Reviewed-by: Denneulin, Guillaume <guillaume.denneulin@intel.com>
Reviewed-by: Rocard, KevinX <kevinx.rocard@intel.com>
Reviewed-by: Centelles, Sylvain <sylvain.centelles@intel.com>
Reviewed-by: Baron, Georges-henriX <georges-henrix.baron@intel.com>
Tested-by: Dixon, CharlesX <charlesx.dixon@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>
diff --git a/xmlserializer/XmlFileDocSource.h b/xmlserializer/XmlFileDocSource.h
index 3274b29..46c5230 100644
--- a/xmlserializer/XmlFileDocSource.h
+++ b/xmlserializer/XmlFileDocSource.h
@@ -40,6 +40,9 @@
     // CXmlDocSource method implemented
     virtual bool populate(CXmlSerializingContext& serializingContext);
 
+    // Check that the file exists and is readable
+    virtual bool isParsable(CXmlSerializingContext& serializingContext) const;
+
 private:
 
     // Validation of the document with the xsd file