Fix opendir NULL dirp return issue

Bug: 206035991
Test: use forrest to run boottest

Change-Id: I9e77b7d6184a0ee132b8f058f7f83302c54bcb4a
diff --git a/modules/sensors/dynamic_sensor/ConnectionDetector.cpp b/modules/sensors/dynamic_sensor/ConnectionDetector.cpp
index c009a70..85b9901 100644
--- a/modules/sensors/dynamic_sensor/ConnectionDetector.cpp
+++ b/modules/sensors/dynamic_sensor/ConnectionDetector.cpp
@@ -156,6 +156,10 @@
 
 void FileConnectionDetector::processExistingFiles() const {
     auto dirp = ::opendir(mPath.c_str());
+    if(dirp == NULL) {
+      ALOGE("Problem open dir %s, errno: %s", mPath.c_str(), ::strerror(errno));
+      return;
+    }
     struct dirent *dp;
     while ((dp = ::readdir(dirp)) != NULL) {
         const std::string name(dp->d_name);