Querying docs with just a cid (no docID) panics

[AndrewSisley]

Documented by TestQuerySimpleWithCid

E.g.:

Request: `query {
	Users (
			cid: "bafyreib7afkd5hepl45wdtwwpai433bhnbd3ps5m2rv3masctda7b6mmxe"
		) {
		name
	}
}`,

When fixing, also test what happens when a collection-level cid is provided, as that is currently untested.

panic: runtime error: index out of range [0] with length 0 [recovered]
panic: runtime error: index out of range [0] with length 0

goroutine 15 [running]:
testing.tRunner.func1.2({0x493f480, 0xc002480150})
/home/andy/go/pkg/mod/golang.org/[email protected]/src/testing/testing.go:1631 +0x24a
testing.tRunner.func1()
/home/andy/go/pkg/mod/golang.org/[email protected]/src/testing/testing.go:1634 +0x377
panic({0x493f480?, 0xc002480150?})
/home/andy/go/pkg/mod/golang.org/[email protected]/src/runtime/panic.go:770 +0x132
github.com/sourcenetwork/defradb/internal/planner.(*selectNode).initSource(0xc0008b5ad0)
/home/andy/Projects/Source/defradb/internal/planner/select.go:270 +0x496
github.com/sourcenetwork/defradb/internal/planner.(*Planner).Select(0xc001736900, 0xc001f904d0)
/home/andy/Projects/Source/defradb/internal/planner/select.go:508 +0x105
github.com/sourcenetwork/defradb/internal/planner.(*Planner).Operation(0xc001736900, 0xc000f37360)
/home/andy/Projects/Source/defradb/internal/planner/operation.go:139 +0x145
github.com/sourcenetwork/defradb/internal/planner.(*Planner).MakePlan(0xc001736900, 0x0?)
/home/andy/Projects/Source/defradb/internal/planner/planner.go:603 +0x65
github.com/sourcenetwork/defradb/internal/planner.(*Planner).RunRequest(0xc001736900, {0x582fbb0, 0xc001ab1020}, 0xc000f37310)
/home/andy/Projects/Source/defradb/internal/planner/planner.go:520 +0x65
github.com/sourcenetwork/defradb/internal/db.(*db).execRequest(0xc001ca8900, {0x582fbb0, 0xc001ab1020}, {0x4dc80c9, 0x80}, 0xc000013ef0)
/home/andy/Projects/Source/defradb/internal/db/request.go:53 +0x65a
github.com/sourcenetwork/defradb/internal/db.(*db).ExecRequest(0xc001ca8900, {0x582fbb0?, 0xc001ab0f90?}, {0x4dc80c9, 0x80}, {0x0, 0x0, 0x8423ce0?})
/home/andy/Projects/Source/defradb/internal/db/store.go:38 +0x25c
github.com/sourcenetwork/defradb/tests/integration.executeRequest(0xc0008f38c8, {{0x0, 0x0}, {0x0, {0x0, 0x0}}, {0x0, 0x0}, {0x0, {0x0, ...}}, ...})
/home/andy/Projects/Source/defradb/tests/integration/utils.go:1853 +0x58c
github.com/sourcenetwork/defradb/tests/integration.performAction(0xc0008f38c8, 0x0?, {0x4a19f00, 0xc000eb2460})
/home/andy/Projects/Source/defradb/tests/integration/utils.go:391 +0xaa5
github.com/sourcenetwork/defradb/tests/integration.executeTestCase({_, }, {, }, {, _, _}, {{0x4c8f62b, 0x1f}, {0xc002040540, ...}, ...}, ...)
/home/andy/Projects/Source/defradb/tests/integration/utils.go:266 +0x1038
github.com/sourcenetwork/defradb/tests/integration.ExecuteTestCase({0x5888eb0, _}, {{0x4c8f62b, 0x1f}, {0xc002040540, 0x3, 0x3}, {0x0, {0x0, 0x0, ...}}, ...})
/home/andy/Projects/Source/defradb/tests/integration/utils.go:214 +0x7e5
github.com/sourcenetwork/defradb/tests/integration/query/simple.TestQuerySimpleWithCid(0xc0020349c0)
/home/andy/Projects/Source/defradb/tests/integration/query/simple/with_cid_test.go:78 +0x38d
testing.tRunner(0xc0020349c0, 0x505ad98)
/home/andy/go/pkg/mod/golang.org/[email protected]/src/testing/testing.go:1689 +0xfb
created by testing.(*T).Run in goroutine 1
/home/andy/go/pkg/mod/golang.org/[email protected]/src/testing/testing.go:1742 +0x390
FAIL github.com/sourcenetwork/defradb/tests/integration/query/simple 0.110s