fix parser EOF after calls with trailing whitespace

[alogic0]

Summary

Fix a parser panic when a completed call is followed by trailing whitespace.

After returning the final apply node, a subsequent Parser.next call could consume trailing whitespace and reach EOF while in the after_call state. The parser then attempted to
calculate the length of an uninitialized path location, causing an integer overflow in Debug builds.

Fix

Return null when EOF is reached in the terminal after_call state with no outstanding call depth.

Tests

Added regression coverage for:

• trailing spaces;
• trailing newline;
• CRLF, tabs, and spaces;
• nested calls followed by a newline.

The test suite passes in Debug and ReleaseSafe modes.