Fix Uninitialized NULL Pointer Dereference Bug in Firmata I2C Message Processing

[arche8]

Bug Description
When I2C SYSEX messages containing the 'v' command byte but without parameters will cause system crashes due to uninitialized NULL pointer dereference in the I2C interrupt handler. When argc = 0, the code performs out-of-bounds access to determine operation mode, enters I2C write branch(https://github.com/firmata/arduino/blob/main/examples/StandardFirmata/StandardFirmata.ino#L510) without buffer allocation, and crashes when the interrupt handler attempts to write through uninitialized txBuffer.

Proposed Fix
Add comprehensive parameter validation in sysexCallback function:

• Validate argc >= 2 before I2C request processing
• Validate argc > 2 for I2C write operations
• Early return with error messages for invalid parameters
• Ensure wireWrite is called to allocate buffers before transmission