panic on non nil "Result" with nil value in "AfterQuery" hook

[server-may-cry]

Query hook receives non nil Result with nil value. This leads to a panic:

runtime error: invalid memory address or nil pointer dereference

Expected Behavior

Code like this don't trigger a nil pointer panic as it have a e.Result != nil check.

func (h hook) AfterQuery(ctx context.Context, e *pg.QueryEvent) error {
	if e.Err != nil {
		h.log("error", e.Err)
	}
	if e.Result != nil {
		h.log("returned", e.Result.RowsReturned())
		h.log("affected", e.Result.RowsAffected())
	}
	return nil
}

Current Behavior

Part of panic stack trace

	/usr/local/go/src/runtime/panic.go:1038 +0x215
github.com/go-pg/pg/v10.(*result).RowsReturned(0xdc4c80)
	/go/pkg/mod/github.com/go-pg/pg/v10@v10.10.6/result.go:52
<REDACTED>.AfterQuery({{0xdae1c0, 0xc00011e110}}, {0xdc4c80, 0xc000b5b7d0}, 0xc0004a1900)
	<REDACTED>.go:110 +0xf2
github.com/go-pg/pg/v10.(*baseDB).afterQueryFromIndex(0xc0000af0e0, {0xdc4c80, 0xc000b5b7d0}, 0x0, 0xdd8890)
	/go/pkg/mod/github.com/go-pg/pg/v10@v10.10.6/hook.go:130 +0x75
github.com/go-pg/pg/v10.(*baseDB).afterQuery(0xc000146d00, {0xdc4c80, 0xc000b5b7d0}, 0xc0009c8005, {0xdbce20, 0x0}, {0xdae1c0, 0xc00011e110})
	/go/pkg/mod/github.com/go-pg/pg/v10@v10.10.6/hook.go:125 +0xaa

Possible Solution

Explicitly set nil for Result when *result is nil.
Related article https://codefibershq.com/blog/golang-why-nil-is-not-always-nil

Steps to Reproduce

1. Add a query hook as provided above
2. Execute SQL which fails
3. nil pointer panic is triggered

Here is an example of how nil becomes not nil https://goplay.tools/snippet/DVV1XNz5icn

Context (Environment)

Detailed Description

On first line res is a nil. At the last line it assigned a value from db.simpleQuery

pg/base.go

Lines 236 to 246 in 51b8018

	var res Result
	var lastErr error
	for attempt := 0; attempt <= db.opt.MaxRetries; attempt++ {
	if attempt > 0 {
	if err := internal.Sleep(ctx, db.retryBackoff(attempt-1)); err != nil {
	return nil, err
	}
	}
	lastErr = db.withConn(ctx, func(ctx context.Context, cn *pool.Conn) error {
	res, err = db.simpleQuery(ctx, cn, wb)

In db.simpleQuery result might get returned with nil value of type *result, but in db.simpleQuery it will be wrapped into Result and will pass != nil check

pg/base.go

Lines 544 to 553 in 51b8018

	var res *result
	if err := cn.WithReader(c, db.opt.ReadTimeout, func(rd *pool.ReaderContext) error {
	var err error
	res, err = readSimpleQuery(rd)
	return err
	}); err != nil {
	return nil, err
	}
	return res, nil

Note: Same issue exists in other parts of a code.

Possible Implementation

Workaround of this issue is to change a hook to look like this:

func (h hook) AfterQuery(ctx context.Context, e *pg.QueryEvent) error {
	if e.Err != nil {
		h.log("error", e.Err)
	} else if e.Result != nil {
		h.log("returned", e.Result.RowsReturned())
		h.log("affected", e.Result.RowsAffected())
	}
	return nil
}