audio/video: Skip preferred drivers when loading a driver on demand

Preferred driver entries have special conditions for initializing, which aren't relevant when a specific driver was explicitly requested.

src/audio/SDL_audio.c

@@ -964,7 +964,7 @@ bool SDL_InitAudio(const char *driver_name)
             }
 
             for (int i = 0; bootstrap[i]; ++i) {
-                if (SDL_strcasecmp(bootstrap[i]->name, driver_attempt) == 0) {
+                if (!bootstrap[i]->is_preferred && SDL_strcasecmp(bootstrap[i]->name, driver_attempt) == 0) {
                     tried_to_init = true;
                     SDL_zero(current_audio);
                     current_audio.pending_events_tail = &current_audio.pending_events;

src/audio/SDL_sysaudio.h

@@ -360,6 +360,7 @@ typedef struct AudioBootStrap
     const char *desc;
     bool (*init)(SDL_AudioDriverImpl *impl);
     bool demand_only; // if true: request explicitly, or it won't be available.
+    bool is_preferred;
 } AudioBootStrap;
 
 // Not all of these are available in a given build. Use #ifdefs, etc.

src/audio/pipewire/SDL_pipewire.c

@@ -1337,7 +1337,7 @@ static bool PIPEWIRE_Init(SDL_AudioDriverImpl *impl)
 }
 
 AudioBootStrap PIPEWIRE_PREFERRED_bootstrap = {
-    "pipewire", "Pipewire", PIPEWIRE_PREFERRED_Init, false
+    "pipewire", "Pipewire", PIPEWIRE_PREFERRED_Init, false, true
 };
 AudioBootStrap PIPEWIRE_bootstrap = {
     "pipewire", "Pipewire", PIPEWIRE_Init, false