stk500v2 bootloader corrupts data when reading EEPROM

When reading EEPROM via avrdude using wiring (via bootloader) - results are corrupted. Every other 8 bytes are lost. Writing to EEPROM works, but, as expected, validation fails as what is written does not match corrupted version that is read back.

You can reproduce on Mega2560(and probably others using this bootloader) using following sketch to initialize EEPROM to known state:

```c++
#include

void eepromDump() {
char buff[8];
int counter = 0;
byte data = 0;
Serial.write("EEPROM contents:\n");
for (int i = 0; i < 4096 ; i++) {
counter = counter % 16;
if (counter == 0) {
snprintf(buff, 10, "%07X", i);
if (i != 0) {
Serial.println();
}
Serial.print(buff);
}
data = EEPROM.read(i);
snprintf(buff, 4, " %02X", data);
Serial.print(buff);
counter ++;
}
Serial.println();
}

void eepromErase(int start){
Serial.println("Erasing EEPROM");
for (int addr=start; addr <4096; addr++){ EEPROM.update(addr, 0x00); }
}

void setup() {
Serial.begin(115200L);
const char data[63]="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
EEPROM.put(0, data);
eepromErase(64);
eepromDump();
}

void loop() {
}
```

After that if executing a read via a programmer you get expected correct output:
```
$ avrdude -c dragon_isp -P usb -p atmega2560 -Ueeprom:r:eeprom.bin:r
$ hexdump -C eeprom.bin
00000000 30 31 32 33 34 35 36 37 38 39 61 62 63 64 65 66 |0123456789abcdef|
00000010 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73 74 75 76 |ghijklmnopqrstuv|
00000020 77 78 79 7a 41 42 43 44 45 46 47 48 49 4a 4b 4c |wxyzABCDEFGHIJKL|
00000030 4d 4e 4f 50 51 52 53 54 55 56 57 58 59 5a 00 ff |MNOPQRSTUVWXYZ..|
00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00001000
```

But using the bootloader for same thing you get corrupted output:

```
$ avrdude -c wiring -P /dev/cu.usbmodem1411 -p atmega2560 -Ueeprom:r:eeprom2.bin:r
$ hexdump -C eeprom2.bin
00000000 30 31 32 33 34 35 36 37 67 68 69 6a 6b 6c 6d 6e |01234567ghijklmn|
00000010 77 78 79 7a 41 42 43 44 4d 4e 4f 50 51 52 53 54 |wxyzABCDMNOPQRST|
00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000800 30 31 32 33 34 35 36 37 67 68 69 6a 6b 6c 6d 6e |01234567ghijklmn|
00000810 77 78 79 7a 41 42 43 44 4d 4e 4f 50 51 52 53 54 |wxyzABCDMNOPQRST|
00000820 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00001000
```

Reproduce the EEPROM read through avrdude with the wiring programmer on a Mega2560, comparing it with the dragon_isp output shown in the issue. Start by reviewing the bootloader work in linked pull request #24 and the EEPROM read path; done means bootloader reads match direct programmer reads and validation succeeds.

Written by the indexing model from the issue text.