i#2557: fix fencepost error in find_free_memory_in_region() (#2559)
i#2557: fix fencepost error in find_free_memory_in_region() (#2559)

Fixes an error where find_free_memory_in_region() thinks that an occupied
region that spans the requested endpoint is free, resulting in an infinite
loop in os_heap_reserve_in_region().

Manually tested on the app whose maps file hit this.  (Creating a suite
test is non-trivial without a mock for the maps iterator.)

Fixes #2557
AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio