SystemInformation: fix potential off-by-one write

in case readlink uses the complete buffer (1024) it will truncate the
result and return 1024 assigned to ll. the subsequent buf[ll] will then be
out of bounds.

the fix assumes, that a truncated result is as useful as experiencing an
error during readlink, hence falling back to /proc/self/exe.

SystemInformation.cxx

@@ -1346,7 +1346,7 @@ std::string SymbolProperties::GetBinary() const
     std::string binary;
     char buf[1024] = { '\0' };
     ssize_t ll = 0;
-    if ((ll = readlink("/proc/self/exe", buf, 1024)) > 0) {
+    if ((ll = readlink("/proc/self/exe", buf, 1024)) > 0 && ll < 1024) {
       buf[ll] = '\0';
       binary = buf;
     } else {