BMesh: decrease decimate epsilon

Since using doubles to calculate cost,
using topology fallback cost isn't needed as much.

source/blender/bmesh/tools/bmesh_decimate_collapse.c

@@ -50,7 +50,7 @@
 /* if the cost from #BLI_quadric_evaluate is 'noise', fallback to topology */
 #define USE_TOPOLOGY_FALLBACK
 #ifdef  USE_TOPOLOGY_FALLBACK
-#  define   TOPOLOGY_FALLBACK_EPS  1e-6f
+#  define   TOPOLOGY_FALLBACK_EPS  FLT_EPSILON
 #endif
 
 /* these checks are for rare cases that we can't avoid since they are valid meshes still */