Motivate of the pull request

Fix issues with the reworked format_ptc_num() function:

• off by one error after split with delimiter
• reusing same stringstream for multiple string to int conversions (clear before using again)

Describe the technical details

What is currently done? (Provide issue link if applicable)

reworked format_ptc_num() function has some issues.

What does this pull request change?

fix the logic in format_ptc_num()

Which part of the code base require a change

• VPR read_route.cpp
• Tileable routing architecture generator
• OpenFPGA libraries
• FPGA-Verilog
• FPGA-Bitstream
• FPGA-SDC
• FPGA-SPICE
• Flow scripts
• Architecture library
• Cell library
• Documentation
• Regression tests
• Continous Integration (CI) scripts

Impact of the pull request

It does not look like it will impact existing cases, but requires review.