n/fractal: increment fractal pos between octave

given summation occurs with only scaling of positions between octaves,
points around the origin are likely to remain self-similar between
octaves. but nudging the point out range of the origin's unit surrounds
we can avoid degenerate highlights.

noise/fractal/fbm.ipp

@@ -67,6 +67,7 @@ namespace util { namespace noise { namespace fractal {
         for (size_t i = 0; i < this->m_octaves; ++i) {
             total += this->m_basis (p) * scale;
 
+            p += T{1};
             p *= this->m_lacunarity;
             scale *= this->m_invGH;
         }

noise/fractal/hetero.ipp

@@ -77,6 +77,7 @@ namespace util { namespace noise { namespace fractal {
 
             result += increment;
 
+            p += T{1};
             p *= this->m_lacunarity;
         }
 

noise/fractal/hmf.ipp

@@ -77,6 +77,7 @@ namespace util { namespace noise { namespace fractal {
             weight  = min (weight, T{1});
 
             scale *= this->m_invGH;
+            p += T{1};
             p *= this->m_lacunarity;
         }
 

noise/fractal/rmf.ipp

@@ -91,6 +91,8 @@ namespace util { namespace noise { namespace fractal {
             result += signal * scale;
 
             scale *= this->m_invGH;
+
+            p += T{1};
             p *= this->m_lacunarity;
         }