fix reading procfs files

old-commit-hash: 6f21993915

selfdrive/common/util.cc

@@ -1,4 +1,5 @@
 #include <errno.h>
+#include <sstream>
 
 #include "common/util.h"
 
@@ -51,11 +52,20 @@ std::string read_file(const std::string& fn) {
   std::ifstream ifs(fn, std::ios::binary | std::ios::ate);
   if (ifs) {
     std::ifstream::pos_type pos = ifs.tellg();
+    if (pos != std::ios::beg) {
       std::string result;
       result.resize(pos);
       ifs.seekg(0, std::ios::beg);
       ifs.read(result.data(), pos);
-    if (ifs) return result;
+      if (ifs) {
+        return result;
+      }
+    } else {
+      // handle files created on read, e.g. procfs
+      std::stringstream buffer;
+      buffer << ifs.rdbuf();
+      return buffer.str();
+    }
   }
   return "";
 }