Code simplification

Simplify the code a bit as suggested:

1) Use unsigned int instead of signed int, so we can avoid checking the
negative case
2) Merge two lines into a single line so we can inline the
implementation

Correct the js sample file header.

testing done:
- Build locally
- Pass -1 as index from js and the code still can correctly handle the
input.

examples/faceBlendCoefficients.js

@@ -1,10 +1,10 @@
 //
-//  coefficients.js
+//  faceBlendCoefficients.js
 //
 //  version 2.0
 //
 //  Created by Bob Long, 9/14/2015
-//  A simple panel that can display the blending coefficients of Avatar's face model.
+//  A simple panel that can select and display the blending coefficient of the Avatar's face model.
 //  
 //  Distributed under the Apache License, Version 2.0.
 //  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html

libraries/render-utils/src/Model.h

@@ -192,9 +192,9 @@ public:
     void setCauterizeBoneSet(const std::unordered_set<int>& boneSet) { _cauterizeBoneSet = boneSet; }
 
     int getBlendshapeCoefficientsNum() const { return _blendshapeCoefficients.size(); }
-    float getBlendshapeCoefficient(int index) const {
-        return index >= _blendshapeCoefficients.size() || index < 0 ?
-               0.0f : _blendshapeCoefficients.at(index); }
+    float getBlendshapeCoefficient(unsigned int index) const {
+        return index >= _blendshapeCoefficients.size() ? 0.0f : _blendshapeCoefficients.at(index);
+     }
 
 protected: