Fix #93; No underscore prefix if envVarsPrefix is empty #360

Job	Run time
build / linux-gcc-14-amd64 (Nim version-2-0)	3m 0s
build / linux-amd64 (Nim devel)	3m 30s
build / linux-amd64 (Nim version-1-6)	2m 0s
build / linux-gcc-14-amd64 (Nim version-1-6)	1m 45s
build / linux-i386 (Nim version-1-6)	2m 33s
build / linux-i386 (Nim version-2-0)	4m 2s
build / windows-amd64 (Nim version-1-6)	4m 31s
build / linux-gcc-14-amd64 (Nim version-2-2)	2m 57s
build / linux-gcc-14-amd64 (Nim devel)	3m 28s
build / windows-amd64 (Nim version-2-0)	5m 10s
build / macos-amd64 (Nim version-1-6)	3m 45s
build / linux-amd64 (Nim version-2-0)	2m 55s
build / macos-arm64 (Nim version-1-6)	2m 26s
build / linux-amd64 (Nim version-2-2)	3m 15s
build / linux-i386 (Nim devel)	4m 42s
build / macos-amd64 (Nim version-2-2)	4m 36s
build / macos-arm64 (Nim version-2-2)	3m 27s
build / windows-amd64 (Nim version-2-2)	4m 29s
build / macos-arm64 (Nim version-2-0)	6m 7s
build / windows-amd64 (Nim devel)	5m 39s
build / macos-arm64 (Nim devel)	3m 38s
build / macos-amd64 (Nim version-2-0)	5m 50s
build / macos-amd64 (Nim devel)	5m 1s
build / linux-i386 (Nim version-2-2)	3m 43s
	1h 32m 29s

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