go/build: remove superfluous continues

This cleanup was proposed in CL 148937. The branch is already ended with
a continue, so remove continues from subbranches and use an else-if.

Change-Id: Iaf6eb57afc84e25862f99a342f5824e315bcdcb7
Reviewed-on: https://go-review.googlesource.com/c/148922Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/go/build/read_test.go

@@ -110,11 +110,8 @@ func testRead(t *testing.T, tests []readTest, read func(io.Reader) ([]byte, erro
 		if err != nil {
 			if tt.err == "" {
 				t.Errorf("#%d: err=%q, expected success (%q)", i, err, string(buf))
-				continue
-			}
-			if !strings.Contains(err.Error(), tt.err) {
+			} else if !strings.Contains(err.Error(), tt.err) {
 				t.Errorf("#%d: err=%q, expected %q", i, err, tt.err)
-				continue
 			}
 			continue
 		}