cmd/go: don't try to print build info of non-Go binaries

On a non-nil err, buildinfo.ReadFile will always return a nil
*Buildinfo. In scanFile, we need to return early if that happens.

Fixes #49181

Change-Id: I354348d206ab084804937c6f922eadb61435e7b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/359154
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/version/version.go

@@ -151,6 +151,7 @@ func scanFile(file string, info fs.FileInfo, mustPrint bool) {
 				fmt.Fprintf(os.Stderr, "%s: %v\n", file, err)
 			}
 		}
+		return
 	}
 
 	fmt.Printf("%s: %s\n", file, bi.GoVersion)

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

@@ -0,0 +1,9 @@
+# test that go version doesn't panic on non-go binaries
+# See Issue #49181
+
+[exec:/bin/true] cp /bin/true true
+[exec:C:\windows\system32\help.exe] cp C:\windows\system32\help.exe help.exe
+
+go version -m .
+! stdout .
+! stderr .