Fix swallowed I/O exception in LcovPrinter

[sputt]

This fixes issue #21982

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[c-mita]

LGTM

[sputt]

Squashed to correct email - no diff.

Functional Test

Coverage roll-up

bazel coverage //tools/test/CoverageOutputGenerator/... --combined_report=lcov --override_repository=bazel_tools~remote_coverage_tools_extension~remote_coverage_tools=/Users/sputt/remote_coverage_tools

To sanity check this is the correct override:

ERROR: /private/var/tmp/_bazel_sputt/b1abbf127d696f148ad833cd4ef695e8/external/bazel_tools/tools/test/BUILD:36:6: @@bazel_tools//tools/test:coverage_report_generator depends on @@bazel_tools~remote_coverage_tools_extension~remote_coverage_tools//:coverage_report_generator in repository @@bazel_tools~remote_coverage_tools_extension~remote_coverage_tools which failed to fetch. no such package '@@bazel_tools~remote_coverage_tools_extension~remote_coverage_tools//': The repository's path is "bazel_tools~remote_coverage_tools_extension~remote_coverage_tools" (absolute: "/Users/sputt/remote_coverage_tools/JUNK") but it does not exist or is not a directory.

Inspect the output report:

ls -l bazel-out/_coverage/_coverage_report.dat 
-r-xr-xr-x  1 sputt  wheel  52981 Apr 13 09:23 bazel-out/_coverage/_coverage_report.dat

All files are present:

cat bazel-out/_coverage/_coverage_report.dat | grep SF:
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/BranchCoverage.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/Constants.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/Coverage.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/GcovJsonParser.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/GcovParser.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/LcovMergerFlags.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/LcovParser.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/LcovPrinter.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/LineCoverage.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/Main.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/Parser.java
SF:tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator/SourceFileCoverage.java

[fmeum]

@bazel-io fork 7.2.0