OpenAL api usage fix

AL_LOOPING should really be set with `alSourcei`

+ fix potential nullptr dereference in `GLRenderAPI::destroyCore`
+ reworded a few docs in BsException.h

Author: nemerle

Source/Plugins/bsfGLRenderAPI/BsGLRenderAPI.cpp

@@ -225,7 +225,8 @@ namespace bs { namespace ct
 		mCurrentDomainProgram = nullptr;
 		mCurrentComputeProgram = nullptr;
 
-		mGLSupport->stop();
+		if (mGLSupport)
+			mGLSupport->stop();
 
 		TextureManager::shutDown();
 		bs::TextureManager::shutDown();

Source/Plugins/bsfOpenAudio/BsOAAudioSource.cpp

@@ -115,7 +115,7 @@ namespace bs
 			if (contexts.size() > 1)
 				alcMakeContextCurrent(contexts[i]);
 
-			alSourcef(mSourceIDs[i], AL_LOOPING, loop);
+			alSourcei(mSourceIDs[i], AL_LOOPING, loop);
 		}
 	}
 
@@ -397,9 +397,9 @@ namespace bs
 			alSourcef(mSourceIDs[i], AL_ROLLOFF_FACTOR, mAttenuation);
 
 			if(requiresStreaming())
-				alSourcef(mSourceIDs[i], AL_LOOPING, false);
+				alSourcei(mSourceIDs[i], AL_LOOPING, false);
 			else
-				alSourcef(mSourceIDs[i], AL_LOOPING, mLoop);
+				alSourcei(mSourceIDs[i], AL_LOOPING, mLoop);
 
 			if (is3D())
 			{