Preserve Writer failures when a template starts at column zero

[allenflux]

When a Writer fails while rendering text at the start of a line, the zero-based template column is passed to HandlebarsError, which requires a positive column. The resulting IllegalArgumentException hides the original write failure reported in #1070.

Normalize the diagnostic column to at least 1, matching HbsErrorReporter, and use it in both the error object and message header. This preserves the original exception as the cause of HandlebarsException without changing Template.position() or positive column values.

One regression test uses a Writer that throws an IOException on the first text write. It fails on the original implementation and passes with this change, checking that the original cause is preserved and the diagnostic column is 1.

Validation on Temurin 21 (Java 17 compilation target):

• mvn -pl handlebars -am test: 1,039 tests, zero failures/errors, 3 existing skips. The baseline ran 1,038 tests with the same skips.
• Spotless check for the two changed files and git diff --check passed.

Fixes #1070.

Implemented with assistance from OpenAI Codex.