cmd/go: avoid duplicate errors in module load

Just a missing base.ExitIfErrors.

Fixes #46160.

Change-Id: I41949b0b7b036da94ba269220951677585d3f8e9
Reviewed-on: https://go-review.googlesource.com/c/go/+/498122
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>

src/cmd/go/internal/modload/load.go

@@ -1056,6 +1056,7 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 			ld.errorf("go: %v\n", err)
 		}
 	}
+	base.ExitIfErrors() // or we will report them again
 
 	for {
 		ld.reset()

src/cmd/go/testdata/script/mod_go_version.txt

@@ -3,11 +3,10 @@
 env GO111MODULE=on
 env TESTGO_VERSION=go1.21
 
-# TODO(rsc): go list prints the error twice. Why?
 ! go list
-stderr '^go: sub@v1.0.0: sub requires go 1.999 \(running go 1.21; go.mod sets go 1.1\)$'
+stderr -count=1 '^go: sub@v1.0.0: sub requires go 1.999 \(running go 1.21; go.mod sets go 1.1\)$'
 ! go build sub
-stderr '^go: sub@v1.0.0: sub requires go 1.999 \(running go 1.21; go.mod sets go 1.1\)$'
+stderr -count=1 '^go: sub@v1.0.0: sub requires go 1.999 \(running go 1.21; go.mod sets go 1.1\)$'
 
 -- go.mod --
 module m

src/cmd/go/testdata/script/mod_tidy_compat_implicit.txt

@@ -51,8 +51,7 @@ stdout '^example.net/lazy v0.1.0$'
 go mod edit -go=1.16
 ! go list -deps -test -f $MODFMT ./...
 
-	# TODO(#46160): -count=1 instead of -count=2.
-stderr -count=2 '^go: example\.net/lazy@v0\.1\.0 requires\n\texample\.com/retract/incompatible@v1\.0\.0: missing go\.sum entry for go\.mod file; to add it:\n\tgo mod download example\.com/retract/incompatible$'
+stderr -count=1 '^go: example\.net/lazy@v0\.1\.0 requires\n\texample\.com/retract/incompatible@v1\.0\.0: missing go\.sum entry for go\.mod file; to add it:\n\tgo mod download example\.com/retract/incompatible$'
 
 
 # If we combine a Go 1.16 go.sum file...

src/cmd/go/testdata/script/mod_tidy_compat_incompatible.txt

@@ -48,8 +48,7 @@ cmp go.mod go.mod.orig
 
 go mod edit -go=1.16
 ! go list -f $MODFMT -deps ./...
-	# TODO(#46160): -count=1 instead of -count=2.
-stderr -count=2 '^go: example\.net/lazy@v0\.1\.0 requires\n\texample\.net/requireincompatible@v0\.1\.0 requires\n\texample\.com/retract/incompatible@v2\.0\.0\+incompatible: missing go.sum entry for go.mod file; to add it:\n\tgo mod download example.com/retract/incompatible$'
+stderr -count=1 '^go: example\.net/lazy@v0\.1\.0 requires\n\texample\.net/requireincompatible@v0\.1\.0 requires\n\texample\.com/retract/incompatible@v2\.0\.0\+incompatible: missing go.sum entry for go.mod file; to add it:\n\tgo mod download example.com/retract/incompatible$'
 
 
 # There are two ways for the module author to bring the two into alignment.

src/cmd/go/testdata/script/mod_tidy_compat_irrelevant.txt

@@ -47,8 +47,7 @@ cmp stdout out-117.txt
 
 go mod edit -go=1.16
 ! go list -deps -test -f $MODFMT all
-	# TODO(#46160): -count=1 instead of -count=2.
-stderr -count=2 '^go: example.net/lazy@v0.1.0 requires\n\texample.com/retract/incompatible@v1.0.0: missing go.sum entry for go.mod file; to add it:\n\tgo mod download example.com/retract/incompatible$'
+stderr -count=1 '^go: example.net/lazy@v0.1.0 requires\n\texample.com/retract/incompatible@v1.0.0: missing go.sum entry for go.mod file; to add it:\n\tgo mod download example.com/retract/incompatible$'
 
 
 -- go.mod --