Fixed an issue in the ProcessMachCore where segments are not always contiguous...

Fixed an issue in the ProcessMachCore where segments are not always contiguous in mach-o core files. We have core files that have segments like:
           Address    Size       File off   File size
           ---------- ---------- ---------- ----------
LC_SEGMENT 0x000f6000 0x00001000 0x1d509ee8 0x00001000 --- ---   0 0x00000000 __TEXT
LC_SEGMENT 0x0f600000 0x00100000 0x1d50aee8 0x00100000 --- ---   0 0x00000000 __TEXT
LC_SEGMENT 0x000f7000 0x00001000 0x1d60aee8 0x00001000 --- ---   0 0x00000000 __TEXT

Any if the user executes the following command:

(lldb) mem read 0xf6ff0

We would attempt to read 32 bytes from 0xf6ff0 but would only get 16 unless we loop through consecutive memory ranges that are contiguous in the address space, but not in the file data.   
                          
This fixes the ProcessMachCore::DoReadMemory() to do the right thing.

<rdar://problem/19729287> 

llvm-svn: 272322