…dalone carriage return

When TextIOWrapper.tell() is called after reading a line that ends with a
standalone carriage return (\r), the tell optimization algorithm incorrectly
assumes there is buffered data to search through. This causes an assertion
failure when skip_back=1 exceeds the empty buffer size.

The fix detects when next_input is empty and skips the optimization phase,
falling back to the byte-by-byte decoding method which always works correctly.
This properly handles the architectural constraint that buffer optimization
cannot function without buffered data.

…dalone carriage return

Add test case and fix assertion failure in TextIOWrapper.tell() when reading
files that end with a standalone carriage return (\r). The optimization
algorithm incorrectly assumed buffered data would always be available,
causing an assertion failure when next_input is empty.

…ndalone carriage return (GH-141331) (GH-141453)

The assertion was checking wrong variable (skip_back vs skip_bytes).
(cherry picked from commit af80fac)

…ndalone carriage return (GH-141331) (GH-141452)

The assertion was checking wrong variable (skip_back vs skip_bytes).
(cherry picked from commit af80fac)

…dalone carriage return (pythonGH-141331)

The assertion was checking wrong variable (skip_back vs skip_bytes).