gopls/internal/golang: add missing err check

Fixes golang/go#74056

Change-Id: I605539185379384bb4f9a034bd0e66fab3e82ffb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/680296
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>

Author: adonovan

gopls/internal/golang/hover.go

@@ -153,7 +153,10 @@ func findRhsTypeDecl(ctx context.Context, snapshot *cache.Snapshot, pkg *cache.P
 		switch o := t.(type) {
 		case *types.Named:
 			obj = o.Obj()
-			declPGF1, declPos1, _ := parseFull(ctx, snapshot, pkg.FileSet(), obj.Pos())
+			declPGF1, declPos1, err := parseFull(ctx, snapshot, pkg.FileSet(), obj.Pos())
+			if err != nil {
+				return "", err
+			}
 			realTypeDecl, _, err := typeDeclContent(declPGF1, declPos1, obj)
 			return realTypeDecl, err
 		}