internal/lsp: fix staticcheck warning

Turns out I had staticcheck off. Maybe we should run it in presubmits...

Change-Id: Ia7089d67ab271af5161b73408df92de818a1ea67
Reviewed-on: https://go-review.googlesource.com/c/tools/+/258720
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
diff --git a/internal/lsp/cache/load.go b/internal/lsp/cache/load.go
index b44be38..01ec4ec 100644
--- a/internal/lsp/cache/load.go
+++ b/internal/lsp/cache/load.go
@@ -118,6 +118,9 @@
 			return err
 		}
 		modContent, err = modFH.Read()
+		if err != nil {
+			return err
+		}
 		var sumFH source.FileHandle
 		if mod.sumURI != "" {
 			sumFH, err = s.GetFile(ctx, mod.sumURI)