[c] Added isNan check that shouldn't care whether the compiler is IEEE compliant or not. Closes #734.

spine-c/spine-c/src/spine/PathConstraint.c

@@ -198,12 +198,17 @@ static void _addAfterPosition (float p, float* temp, int i, float* out, int o) {
 	out[o + 2] = r;
 }
 
+static int _isNan(float value) {
+	float _nan =  (float)0.0/(float)0.0;
+	return 0 == memcmp((void*)&value, (void*)&_nan, sizeof(value));
+}
+
 static void _addCurvePosition (float p, float x1, float y1, float cx1, float cy1, float cx2, float cy2, float x2, float y2,
 		float* out, int o, int/*bool*/tangents) {
 	float tt, ttt, u, uu, uuu;
 	float ut, ut3, uut3, utt3;
 	float x, y;
-	if (p == 0) p = 0.0001f;
+	if (p == 0 || _isNan(p)) p = 0.0001f;
 	tt = p * p, ttt = tt * p, u = 1 - p, uu = u * u, uuu = uu * u;
 	ut = u * p, ut3 = ut * 3, uut3 = u * ut3, utt3 = ut3 * p;
 	x = x1 * uuu + cx1 * uut3 + cx2 * utt3 + x2 * ttt, y = y1 * uuu + cy1 * uut3 + cy2 * utt3 + y2 * ttt;