Free decoder bin if error occurs during setup.

In the case that an error occurs in ReplaceDecodeBin before the bin is added to
the pipeline, unreference the object to allow cleanup. This change also separates
CreateDecodeBinFromUrl from ReplaceDecodeBin, following the pattern of
CreateDecodeBinFromString.

src/engines/gstenginepipeline.cpp

@@ -153,17 +153,28 @@ bool GstEnginePipeline::ReplaceDecodeBin(GstElement* new_bin) {
 }
 
 bool GstEnginePipeline::ReplaceDecodeBin(const QUrl& url) {
-  GstElement* new_bin = nullptr;
+  GstElement* new_bin = CreateDecodeBinFromUrl(url);
+  return ReplaceDecodeBin(new_bin);
+}
 
+GstElement* GstEnginePipeline::CreateDecodeBinFromUrl(const QUrl& url) {
+  GstElement* new_bin = nullptr;
 #ifdef HAVE_SPOTIFY
   if (url.scheme() == "spotify") {
     new_bin = gst_bin_new("spotify_bin");
+    if (!new_bin) return nullptr; 
 
     // Create elements
     GstElement* src = engine_->CreateElement("tcpserversrc", new_bin);
-    if (!src) return false;
+    if (!src) {
+      gst_object_unref(GST_OBJECT(new_bin));
+      return nullptr;
+    }
     GstElement* gdp = engine_->CreateElement("gdpdepay", new_bin);
-    if (!gdp) return false;
+    if (!gdp) {
+      gst_object_unref(GST_OBJECT(new_bin));
+      return nullptr;
+    }
 
     // Pick a port number
     const int port = Utilities::PickUnusedPort();
@@ -188,7 +199,7 @@ bool GstEnginePipeline::ReplaceDecodeBin(const QUrl& url) {
   } else {
 #endif
     new_bin = engine_->CreateElement("uridecodebin");
-    if (!new_bin) return false;
+    if (!new_bin) return nullptr; 
     g_object_set(G_OBJECT(new_bin), "uri", url.toEncoded().constData(),
                  nullptr);
     CHECKED_GCONNECT(G_OBJECT(new_bin), "drained", &SourceDrainedCallback,
@@ -200,7 +211,7 @@ bool GstEnginePipeline::ReplaceDecodeBin(const QUrl& url) {
   }
 #endif
 
-  return ReplaceDecodeBin(new_bin);
+  return new_bin;
 }
 
 GstElement* GstEnginePipeline::CreateDecodeBinFromString(const char* pipeline) {
@@ -474,7 +485,10 @@ bool GstEnginePipeline::InitFromString(const QString& pipeline) {
     return false;
   }
 
-  if (!ReplaceDecodeBin(new_bin)) return false;
+  if (!ReplaceDecodeBin(new_bin)) {
+    gst_object_unref(GST_OBJECT(new_bin));
+    return false;
+  }
 
   if (!Init()) return false;
   return gst_element_link(new_bin, audiobin_);

src/engines/gstenginepipeline.h

@@ -151,6 +151,7 @@ signals:
 
   bool Init();
   GstElement* CreateDecodeBinFromString(const char* pipeline);
+  GstElement* CreateDecodeBinFromUrl(const QUrl& url);
 
   void UpdateVolume();
   void UpdateEqualizer();