fix(voip-mumble): nullptr check

This fixes a nullptr exception when trying to write to the Audio Processing Module while the audioCaptureClient is invalid.

code/components/voip-mumble/src/MumbleAudioInput.cpp

@@ -139,22 +139,26 @@ void MumbleAudioInput::ThreadFunc()
 
 		if (g_curInputIntentMode != g_lastIntentMode)
 		{
-			switch (g_curInputIntentMode)
-			{
-			case InputIntentMode::MUSIC:
-			{
-				m_apm->noise_suppression()->Enable(false);
-				m_apm->high_pass_filter()->Enable(false);
-				break;
-			}
-			case InputIntentMode::SPEECH:
-			default:
+			if (m_apm)
 			{
-				m_apm->noise_suppression()->Enable(true);
-				m_apm->high_pass_filter()->Enable(true);
-				break;
+				switch (g_curInputIntentMode)
+				{
+				case InputIntentMode::MUSIC:
+				{
+					m_apm->noise_suppression()->Enable(false);
+					m_apm->high_pass_filter()->Enable(false);
+					break;
+				}
+				case InputIntentMode::SPEECH:
+				default:
+				{
+					m_apm->noise_suppression()->Enable(true);
+					m_apm->high_pass_filter()->Enable(true);
+					break;
+				}
+				};
 			}
-			};
+
 			g_lastIntentMode = g_curInputIntentMode;
 		}