GH-49752: [C++][Gandiva] Fix potential buffer overrun in Gandiva SSL function #6207

Job	Run time
check-labels / Check labels	23s
ODBC Linux	0s
ODBC ${{ matrix.build-type }} ${{ matrix.architecture }} macOS ${{ matrix.macos-version }}	0s
JNI ${{ matrix.platform.runs-on }} ${{ matrix.platform.arch }}	0s
ODBC Windows	0s
JNI macOS	0s
matrix.title	0s
ODBC release	-1s
ODBC nightly	-1s
report-extra-cpp	-1s
ARM64 Windows 11 MSVC	-1s
	19s

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