libvaladoc/girimporter: Don't guess length of xml header, iterate forward to <repository>

If e.g. the xml header is missing, it resulted in errors like:

    error: expected start element of `repository'
    error: unsupported GIR version (null) (supported: 1.2)

1 files changed, 7 insertions, 3 deletions

diff --git a/libvaladoc/importer/girdocumentationimporter.vala b/libvaladoc/importer/girdocumentationimporter.vala
index b7d475043..e0ae01d6c 100644
--- a/libvaladoc/importer/girdocumentationimporter.vala
+++ b/libvaladoc/importer/girdocumentationimporter.vala
@@ -69,10 +69,14 @@ public class Valadoc.Importer.GirDocumentationImporter : DocumentationImporter {
 		this.reader = new Vala.MarkupReader (source_file);
 
 		// xml prolog
-		next ();
-		next ();
+		do {
+			next ();
+			if (current_token == Vala.MarkupTokenType.EOF) {
+				error ("unexpected end of file");
+				return;
+			}
+		} while (current_token != Vala.MarkupTokenType.START_ELEMENT && reader.name != "repository");
 
-		next ();
 		parse_repository ();
 
 		reader = null;