[Matlab] Fix definition of isFlow

Caused most Matlab flame simulations to fail, e.g. those using
CounterFlowDiffusionFlame.m or flame.m. Fixes regression introduced in c1067aa.

Fixes #554

interfaces/matlab/toolbox/1D/@Domain1D/isFlow.m

@@ -8,7 +8,9 @@ function a = isFlow(d)
 %
 
 t = domainType(d);
-if t == 50
+
+% See Domain1D.h for definitions of constants
+if t < 100
     a = 1;
 else
     a = 0;