Fix FindConfig in cros_component_installed_chromeos

The CL fixes FindConfig implementation to return nullptr for unknown
components.
FindConfig used std::find_if to find a matching component config. For
non-existing elements, find_if returns the last iterator (in this case
std::end(kConfigs)), which is invalid, but non-null.

BUG=None

Change-Id: I53ff08d43131d4f8bfd02c8e02347de095ed6094
Reviewed-on: https://chromium-review.googlesource.com/1164581Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581262}

chrome/browser/component_updater/cros_component_installer_chromeos.cc

@@ -47,9 +47,12 @@ const ComponentConfig kConfigs[] = {
 };
 
 const ComponentConfig* FindConfig(const std::string& name) {
-  return std::find_if(
+  const ComponentConfig* config = std::find_if(
       std::begin(kConfigs), std::end(kConfigs),
       [&name](const ComponentConfig& config) { return config.name == name; });
+  if (config == std::end(kConfigs))
+    return nullptr;
+  return config;
 }
 
 // TODO(xiaochu): add metrics for component usage (https://crbug.com/793052).