Fix seeking with some http streamed content

Do not rely on the URL to determine if we can seek in media. Instead try to seek to the start, if no error occurs: we can seek.
This allows seeking in a youtube stream using AirPlay

mythtv/libs/libmythtv/streamingringbuffer.cpp

@@ -1,4 +1,3 @@
-#include <QUrl>
 #include "mythcorecontext.h"
 #include "mythlogging.h"
 
@@ -48,19 +47,18 @@ bool StreamingRingBuffer::OpenFile(const QString &lfilename, uint retry_ms)
     filename = lfilename;
 
     // TODO check whether local area file
-    QUrl url(filename);
-    QString ext = filename.right(3).toLower();
-    if (url.scheme().toLower() == "http" && (ext == "mp4" || ext == "m4v"))
+
+    int res = url_open(&m_context, filename.toAscii(), URL_RDONLY);
+    if (res >=0 && m_context &&
+        (!m_context->is_streamed && url_seek(m_context, 0, SEEK_SET) >= 0))
     {
+        m_streamed   = false;
         m_allowSeeks = true;
-        m_streamed   = false; // yes - counterintuitive
     }
 
     LOG(VB_GENERAL, LOG_INFO, LOC + QString("Trying %1 (allow seeks: %2")
         .arg(filename).arg(m_allowSeeks));
 
-    int res = url_open(&m_context, filename.toAscii(), URL_RDONLY);
-
     rwlock.unlock();
 
     if (res < 0 || !m_context)