Small changes to C API unit tests.

- (1) Changed randomized math structure values to predefined values to prevent cases that could potentially lead to division by zero.
- (2) Removed unused variable(s) due to (1).
- (3) Renamed variable(s) for better clarity.

test/unit/MathTest.cpp

@@ -47,13 +47,10 @@ namespace Assimp {
 // Initialize epsilon value.
 const float AssimpMathTest::Epsilon = Math::getEpsilon<float>();
 
-// Initialize with an interval of [1,100] to avoid null values.
-RandomUniformFloatGenerator AssimpMathTest::Rand(1.0f, 100.0f);
+// Initialize with an interval of [1,100].
+RandomUniformFloatGenerator AssimpMathTest::RandNonZero(1.0f, 100.0f);
 
 // Initialize with an interval of [-PI,PI] inclusively.
 RandomUniformFloatGenerator AssimpMathTest::RandPI(-Math::PI<float>(), Math::PI<float>());
 
-// Initialize with an interval of [0,1] inclusively.
-RandomUniformFloatGenerator AssimpMathTest::RandUnit(0.0f, 1.0f);
-
 }