AudioDriverPulseAudio: move Vector Cow access outside tight loop.

Replaced some in-loop uses of Vector.write with an out of loop ptrw,
to avoid a lot of superfluous reads on the CowData ref count.

(cherry picked from commit 47496a55bc54dd1aca15d30158e14703b0670f36)

drivers/pulseaudio/audio_driver_pulseaudio.cpp

@@ -381,16 +381,18 @@ void AudioDriverPulseAudio::thread_func(void *p_udata) {
 			ad->lock();
 			ad->start_counting_ticks();
 
+			int16_t *out_ptr = ad->samples_out.ptrw();
+
 			if (!ad->active) {
 				for (unsigned int i = 0; i < ad->pa_buffer_size; i++) {
-					ad->samples_out.write[i] = 0;
+					out_ptr[i] = 0;
 				}
 			} else {
 				ad->audio_server_process(ad->buffer_frames, ad->samples_in.ptrw());
 
 				if (ad->channels == ad->pa_map.channels) {
 					for (unsigned int i = 0; i < ad->pa_buffer_size; i++) {
-						ad->samples_out.write[i] = ad->samples_in[i] >> 16;
+						out_ptr[i] = ad->samples_in[i] >> 16;
 					}
 				} else {
 					// Uneven amount of channels
@@ -399,11 +401,11 @@ void AudioDriverPulseAudio::thread_func(void *p_udata) {
 
 					for (unsigned int i = 0; i < ad->buffer_frames; i++) {
 						for (int j = 0; j < ad->pa_map.channels - 1; j++) {
-							ad->samples_out.write[out_idx++] = ad->samples_in[in_idx++] >> 16;
+							out_ptr[out_idx++] = ad->samples_in[in_idx++] >> 16;
 						}
 						uint32_t l = ad->samples_in[in_idx++] >> 16;
 						uint32_t r = ad->samples_in[in_idx++] >> 16;
-						ad->samples_out.write[out_idx++] = (l + r) / 2;
+						out_ptr[out_idx++] = (l + r) / 2;
 					}
 				}
 			}