Fix Freeboy noise channel playback (#4538)

Writing the enable bit to `FF23` causes the noise oscillator to start outputting samples and writing the other registers (including the one for the SRW value) during the time the oscillator is active has undefined behaviour.
In order for `GB_apu` to correctly generate samples when the LSFR width is
set to `7`, the trigger write to `0xff23` must happen after all other
writes.

plugins/papu/papu_instrument.cpp

@@ -276,9 +276,6 @@ void papuInstrument::playNote( NotePlayHandle * _n,
 		data += m_ch4SweepStepLengthModel.value();
 		papu->write_register( 0xff21, data );
 
-		//channel 4 init
-		papu->write_register( 0xff23, 128 );
-
 		_n->m_pluginData = papu;
 	}
 
@@ -380,6 +377,10 @@ void papuInstrument::playNote( NotePlayHandle * _n,
 		data = data << 3;
 		data += ropt;
 		papu->write_register( 0xff22, data );
+
+		//channel 4 init
+		papu->write_register( 0xff23, 128 );
+
 	}
 
 	int const buf_size = 2048;