one more warning fix #268

Job	Run time
ubuntu-latest\|debug\|--enable-mcsat\|CC=gcc CXX=g++	8m 17s
ubuntu-latest\|debug\|--enable-mcsat\|CC=clang CXX=clang++	8m 14s
ubuntu-latest\|debug\|--enable-thread-safety\|CC=gcc CXX=g++	4m 42s
ubuntu-latest\|debug\|--enable-thread-safety\|CC=clang CXX=clang++	4m 29s
ubuntu-latest\|release\|--enable-mcsat\|CC=gcc CXX=g++	4m 57s
ubuntu-latest\|release\|--enable-mcsat\|CC=clang CXX=clang++	4m 57s
ubuntu-latest\|release\|--enable-thread-safety\|CC=gcc CXX=g++	2m 3s
ubuntu-latest\|release\|--enable-thread-safety\|CC=clang CXX=clang++	3m 45s
ubuntu-latest\|gcov\|--enable-mcsat\|CC=gcc CXX=g++	8m 44s
ubuntu-latest\|debug\|--enable-thread-safety --enable-mcsat\|CC=gcc CXX=g++	7m 43s
	57m 51s

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