Hoikas' fix for crash when triggering missing animation

https://github.com/H-uru/Plasma/pull/103

Sources/Plasma/PubUtilLib/plAvatar/plAnimStage.cpp

@@ -424,6 +424,14 @@ bool plAnimStage::IMoveBackward(double time, float delta, float &overrun, plArma
 	bool infiniteLoop = fLoops == -1;
 	bool loopsRemain = fCurLoop > 0 || infiniteLoop;
 
+	// If we don't have this animation, just pretend to have worked.
+	// Otherwise, we crash the client.
+	if (!fAnimInstance)
+	{
+		hsAssert(false, "AnimInstance nil");
+		return true;
+	}
+
 	// This must be here before we set the local time.
 	if (fAnimInstance->GetTimeConvert())
 		fAnimInstance->GetTimeConvert()->Backwards();
@@ -476,6 +484,14 @@ bool plAnimStage::IMoveForward(double time, float delta, float &overrun, plArmat
 	// first get the target time in local time, ignoring overruns
 	float target = fLocalTime + delta;
 
+	// If we don't have this animation, just pretend to have worked.
+	// Otherwise, we crash the client.
+	if (!fAnimInstance)
+	{
+		hsAssert(false, "AnimInstance nil");
+		return true;
+	}
+
 	if (fAnimInstance->GetTimeConvert())
 		fAnimInstance->GetTimeConvert()->Forewards();