Fix: special elf program header with zero p_filesz

[andelf]

Fix #77

This might also affect probe-rs.

The original defect is that the object crate returns an Error accessing data when p_filesz of a ProgramHeader is zero. (I belive it should return an empty slice).

In case #77: the second ProgramHeader's p_filesz is zero.

firmware.elf:     file format elf32-littleriscv

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .init         00000004  00000000  00000000  00001000  2**1
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .vector       00000004  00000004  00000004  00001004  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  2 .text         000001e4  00000008  00000008  00001008  2**1
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  3 .fini         00000000  000001ec  000001ec  000011ec  2**0
                  CONTENTS, ALLOC, LOAD, CODE

=> The above sections belong to the first ProgramHeader.
  p_vaddr: U32(0), p_paddr: U32(0), p_filesz: U32(1ec), p_memsz: U32(1ec)
=> The following sections belong to the second ProgramHeader.
  p_vaddr: U32(20000000), p_paddr: U32(1ec), p_filesz: U32(0), p_memsz: U32(4)

  4 .dalign       00000000  20000000  20000000  000011ec  2**0
                  CONTENTS
  5 .dlalign      00000000  000001ec  000001ec  000011ec  2**0
                  CONTENTS
  6 .data         00000000  20000000  20000000  000011ec  2**0
                  CONTENTS, ALLOC, LOAD, DATA
  7 .bss          00000004  20000000  000001ec  00002000  2**2
                  ALLOC
  8 .comment      00000033  00000000  00000000  000011ec  2**0
                  CONTENTS, READONLY

CC @maxgerhardt

[andelf]

@maxgerhardt Once you confirm the fix works, I'll proceed with a new release.

[maxgerhardt]

Confirmed, with the latest version from this CI I get this

C:\Users\Max>"C:\Users\Max\Downloads\wlink-win-x86(1)\wlink.exe" flash C:\Users\Max\Downloads\blink\firmware.elf
08:37:35 [INFO] Connected to WCH-Link v2.14(v34) (WCH-LinkE-CH32V305)
08:37:35 [INFO] Attached chip: CH32X035 [CH32X035F8U6] (ChipID: 0x035e0601)
08:37:35 [INFO] Chip ESIG: FlashSize(62KB) UID(cd-ab-28-c5-49-bc-3e-2d)
08:37:35 [INFO] Flash protected: false
08:37:35 [INFO] Read C:\Users\Max\Downloads\blink\firmware.elf as ELF format
08:37:35 [INFO] Flashing 492 bytes to 0x08000000
08:37:35 [INFO] Read protected: false
████████████████████████████████████████████████████████████████████████████████████████████████████████████████ 492/492
08:37:35 [INFO] Flash done
08:37:35 [INFO] Now reset...

[andelf]

Released as v0.1.1.