Fix slice bounds out of range

[fridim]

see GPTEINFRA-3300

This change fixes the following error that occurs when there are
multiple slice reductions to execute:

panic: runtime error: slice bounds out of range [8:7]

goroutine 1 [running]:
main.strategicCleanupSlice({0xc000448800, 0xd, 0x1?})
        /home/fridim/sync/dev/agnosticv-public/cli/strategic_merge.go:33 +0x67d
main.strategicCleanupMap(0x7287c0?)
        /home/fridim/sync/dev/agnosticv-public/cli/strategic_merge.go:62 +0x194
main.strategicMerge(0xc000386ea0, 0x7a05c4?)
        /home/fridim/sync/dev/agnosticv-public/cli/strategic_merge.go:86 +0xca
main.customStrategyMerge(0xc0003d2180?, 0xc00043b6f8?, {{0xc0002ec9b0?, 0x7?}, {0xc0002ec9a0?, 0x0?}})
        /home/fridim/sync/dev/agnosticv-public/cli/merge.go:214 +0xd85
main.mergeVars({0xc0003c4210, 0x24}, {0xc00038b180, 0x3, 0x519daa?})
        /home/fridim/sync/dev/agnosticv-public/cli/merge.go:284 +0x7ad
main.findCatalogItems.func1({0xc0003c4210, 0x24}, {0x82fa48?, 0xc00033c820?}, {0x0?, 0x0?})
        /home/fridim/sync/dev/agnosticv-public/cli/agnosticv.go:243 +0x32f
path/filepath.walk({0xc0003c4210, 0x24}, {0x82fa48, 0xc00033c820}, 0xc00043be10)
        /usr/lib/go/src/path/filepath/path.go:418 +0x123
path/filepath.walk({0xc0004c4180, 0x1b}, {0x82fa48, 0xc00033c0d0}, 0xc00043be10)
        /usr/lib/go/src/path/filepath/path.go:442 +0x285
path/filepath.walk({0xc0003f61e8, 0x4}, {0x82fa48, 0xc000313ee0}, 0xc00043be10)
        /usr/lib/go/src/path/filepath/path.go:442 +0x285
path/filepath.walk({0x7995f8, 0x1}, {0x82fa48, 0xc0004c69c0}, 0xc00043be10)
        /usr/lib/go/src/path/filepath/path.go:442 +0x285
path/filepath.Walk({0x7995f8, 0x1}, 0xc000175e10)
        /usr/lib/go/src/path/filepath/path.go:505 +0x6c
main.findCatalogItems({0xc00001c094, 0x1f}, {0xc000099960, 0x1, 0x1}, {0x0, 0x0, 0x0}, {0x0, 0x0, ...})
        /home/fridim/sync/dev/agnosticv-public/cli/agnosticv.go:219 +0x272
main.main()
        /home/fridim/sync/dev/agnosticv-public/cli/agnosticv.go:491 +0x15c