Enable filter hotswap, extra debug line, small doc fix

Author: devoxin

IMPLEMENTATION.md

@@ -123,7 +123,7 @@ Using the player equalizer
     ]
 }
 ```
-There are 16 bands (0-15) that can be changed.
+There are 15 bands (0-14) that can be changed.
 `gain` is the multiplier for the given band. The default value is 0. Valid values range from -0.25 to 1.0,
 where -0.25 means the given band is completely muted, and 0.25 means it is doubled. Modifying the gain could
 also change the volume of the output.

LavalinkServer/src/main/java/lavalink/server/config/AudioPlayerConfiguration.java

@@ -45,6 +45,8 @@ public Supplier<AudioPlayerManager> audioPlayerManagerSupplier(AudioSourcesConfi
             if (sources.isHttp()) audioPlayerManager.registerSourceManager(new HttpAudioSourceManager());
             if (sources.isLocal()) audioPlayerManager.registerSourceManager(new LocalAudioSourceManager());
 
+            audioPlayerManager.getConfiguration().setFilterHotSwapEnabled(true);
+
             return audioPlayerManager;
         };
     }

LavalinkServer/src/main/java/lavalink/server/player/Player.java

@@ -91,6 +91,7 @@ public void setVolume(int volume) {
     }
 
     public void setBandGain(int band, float gain) {
+        log.debug("Setting band {}'s gain to {}", band, gain);
         equalizerFactory.setGain(band, gain);
 
         if (gain == 0.0f) {
@@ -110,7 +111,7 @@ public void setBandGain(int band, float gain) {
                 this.player.setFilterFactory(null);
                 this.isEqualizerApplied = false;
             }
-        } else {
+        } else if (!this.isEqualizerApplied) {
             this.player.setFilterFactory(equalizerFactory);
             this.isEqualizerApplied = true;
         }