stek_share: resize instead of reserve (#10793)

stek_share indexes into an offset on a string that it reserved space
for, but indexing past size() is undefined behavior. This would result
in crashing on some systems. reszing adjusts the length which satisfies
the indexing requirement.

plugins/experimental/stek_share/common.cc

@@ -36,7 +36,7 @@ std::string
 hex_str(std::string const &str)
 {
   std::string hex_str;
-  hex_str.reserve(str.size() * 2);
+  hex_str.resize(str.size() * 2);
   for (unsigned long int i = 0; i < str.size(); ++i) {
     unsigned char c    = str.at(i);
     hex_str[i * 2]     = hex_chars[(c & 0xF0) >> 4];