remove check for xml header as too many xhtml files are missing it

src/BookManipulation/XhtmlDoc.cpp

@@ -280,15 +280,13 @@ XhtmlDoc::WellFormedError XhtmlDoc::GumboWellFormedErrorForSource(const QString
 XhtmlDoc::WellFormedError XhtmlDoc::WellFormedErrorForSource(const QString &source, QString version)
 {
     QXmlStreamReader reader(source);
-    int nxmlheaders = 0;
     int ndoctypes = 0;
     int nhtmltags = 0;
     int nheadtags = 0;
     int nbodytags = 0;
 
     while (!reader.atEnd()) {
         reader.readNext();
-        if (reader.isStartDocument()) nxmlheaders++;
         if (reader.isDTD()) ndoctypes++;
         if (reader.isStartElement()) {
             if (reader.name() == "html") nhtmltags++;
@@ -304,13 +302,6 @@ XhtmlDoc::WellFormedError XhtmlDoc::WellFormedErrorForSource(const QString &sour
         return error;
     }
     // make sure basic structure in place
-    if (nxmlheaders != 1) {
-        XhtmlDoc::WellFormedError error;
-        error.line    = 1;
-        error.column  = 1;
-        error.message = "Missing xml header";
-        return error;
-    }
     if (ndoctypes != 1) {
         XhtmlDoc::WellFormedError error;
         error.line    = 1;

src/Importers/ImportEPUB.cpp

@@ -197,8 +197,8 @@ QSharedPointer<Book> ImportEPUB::GetBook(bool extract_metadata)
         if (QMessageBox::Yes == QMessageBox::warning(QApplication::activeWindow(),
                 tr("Sigil"),
                 tr("This EPUB has HTML files that are not well formed or are "
-                   "missing a xml header, DOCTYPE, html, head or body "
-                   "elements. Sigil can automatically fix these files, although "
+                   "missing a DOCTYPE, html, head or body elements. "
+                   "Sigil can automatically fix these files, although "
                    "this may result in minor data loss in extreme circumstances.\n\n"
                    "Do you want to automatically fix the files?"),
                 QMessageBox::Yes|QMessageBox::No))