rect: Fix compiler errors about uninitialized use of variables

rect: Fix compiler errors about uninitialized use of variables

error: 'r2.x' may be used uninitialized in this function

Its happening when using gcc 5.3 with musl C library. its considering
the case when case falls into default and immediately after exiting
this there is a check if (r1.h > 0 && r1.w > 0) where r1 element is
used but not assigned anything.

GCC is not noticing the control flow where the initilization will
always work due to assertion call can be a function call from libc

Signed-off-by: Khem Raj <raj.khem@gmail.com>