doxygen: add newline after \file

While \file doesn't need an argument, it can't have another doxy
command after it.

source/blender/python/mathutils/mathutils_geometry.h

@@ -17,7 +17,8 @@
 #ifndef __MATHUTILS_GEOMETRY_H__
 #define __MATHUTILS_GEOMETRY_H__
 
-/** \file \ingroup pymathutils
+/** \file
+ * \ingroup pymathutils
  */
 
 PyMODINIT_FUNC PyInit_mathutils_geometry(void);