Fix divide by zero causing NaN with certain day cycles in DRTVWR-559

indra/llinventory/llsettingsbase.cpp

@@ -693,6 +693,7 @@ void LLSettingsBlender::update(const LLSettingsBase::BlendFactor& blendf)
 F64 LLSettingsBlender::setBlendFactor(const LLSettingsBase::BlendFactor& blendf_in)
 {
     LLSettingsBase::TrackPosition blendf = blendf_in;
+    llassert(!isnan(blendf));
     if (blendf >= 1.0)
     {
         triggerComplete();

indra/llinventory/llsettingsbase.h

@@ -467,6 +467,7 @@ protected:
 
 class LLSettingsBlenderTimeDelta : public LLSettingsBlender
 {
+protected:
     LOG_CLASS(LLSettingsBlenderTimeDelta);
 public:
     static const LLSettingsBase::BlendFactor MIN_BLEND_DELTA;

indra/newview/llenvironment.cpp

@@ -168,6 +168,9 @@ namespace
     // Find normalized track position of given time along full length of cycle
     inline LLSettingsBase::TrackPosition convert_time_to_position(const LLSettingsBase::Seconds& time, const LLSettingsBase::Seconds& len)
     {
+        // early out to avoid divide by zero.  if len is zero then jump to end position
+        if (len == 0.f) return 1.f;
+
         LLSettingsBase::TrackPosition position = LLSettingsBase::TrackPosition(fmod((F64)time, (F64)len) / (F64)len);
         return llclamp(position, 0.0f, 1.0f);
     }