Fix missing load bias.

There are binaries that have non-executable LOAD with p_offset=0.

E.g.,

Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  PHDR           0x000040 0x0000000000400040 0x0000000000400040 0x0002a0 0x0002a0 R   0x8
  INTERP         0x0002e0 0x00000000004002e0 0x00000000004002e0 0x00001c 0x00001c R   0x1
      [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
  LOAD           0x000000 0x0000000000400000 0x0000000000400000 0x0059e0 0x0059e0 R   0x1000
  LOAD           0x006000 0x0000000000406000 0x0000000000406000 0x10f2b05 0x10f2b05 R E 0x1000
  LOAD           0x10f9000 0x00000000014f9000 0x00000000014f9000 0x70f634 0x70f634 R   0x1000
  LOAD           0x1808f18 0x0000000001c09f18 0x0000000001c09f18 0x089fc8 0x0a7ab8 RW  0x1000
  DYNAMIC        0x1864ce0 0x0000000001c65ce0 0x0000000001c65ce0 0x000240 0x000240 RW  0x8
  NOTE           0x0002fc 0x00000000004002fc 0x00000000004002fc 0x000020 0x000020 R   0x4
  TLS            0x1808f18 0x0000000001c09f18 0x0000000001c09f18 0x000010 0x000010 R   0x8
  GNU_EH_FRAME   0x11abde8 0x00000000015abde8 0x00000000015abde8 0x14484c 0x14484c R   0x4
  GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RWE 0x10
  GNU_RELRO      0x1808f18 0x0000000001c09f18 0x0000000001c09f18 0x05c0e8 0x05c0e8 R   0x1

Test: host libunwindstack_test passes.
Test: Modified unit tests and new offline test.

Change-Id: I3992f712be238c7d4109556580b5dcc71175fe19