gpg4libre: Handle error when retrieving public key

Change-Id: I9543e47fb3302a5ca146a606305b24733f015a5d

xmlsecurity/source/gpg/CertificateImpl.cxx

@@ -211,7 +211,10 @@ void CertificateImpl::setCertificate(GpgME::Context* ctx, const GpgME::Key& key)
 
     // extract key data, store into m_aBits
     GpgME::Data data_out;
-    ctx->exportPublicKeys(key.keyID(), data_out);
+    GpgME::Error err = ctx->exportPublicKeys(key.keyID(), data_out);
+
+    if (err)
+        throw RuntimeException("The GpgME library failed to retrieve the public key");
 
     assert(data_out.seek(0,SEEK_SET) == 0);
     int len=0, curr=0; char buf;