metal_chem parser OOB on blank/comment lines

metal_chem table parser can read out-of-bounds on blank/comment-only input

Summary

actual_network_init() in networks/metal_chem/actual_network_data.cpp assumes each scanned line has at least one character while skipping comments (line[0] != '#'). A blank line can trigger out-of-bounds access, and a comment-only/EOF file path gives weak validation behavior.

Severity

High

Affected Code

• networks/metal_chem/actual_network_data.cpp
  • comment-skip loop around line 28
  • header validation around lines 35-36

Why This Is a Bug

• Accessing line[0] when line.empty() is undefined behavior.
• If the file has only comments or terminates before a data header, the current flow does not robustly detect that no header was found before checking format.
• This is initialization-path code; failure can abort setup or silently misdiagnose malformed inputs.

Proposed Patch

Harden parsing by:

1. Ignoring empty lines while scanning for header.
2. Tracking whether a non-comment header line was found.
3. Throwing a clear error if missing header before format checks.

--- a/networks/metal_chem/actual_network_data.cpp
+++ b/networks/metal_chem/actual_network_data.cpp
@@
-    // Skip comments and read until the first non-comment line
-    while (std::getline(file, line)) {
-        if (line[0] != '#') {
-            break;
-        }
-    }
+    // Skip comments/blank lines and read until the first data/header line
+    bool found_header = false;
+    while (std::getline(file, line)) {
+        if (line.empty()) {
+            continue;
+        }
+        if (line[0] == '#') {
+            continue;
+        }
+        found_header = true;
+        break;
+    }
+
+    if (!found_header) {
+        throw std::runtime_error("ERROR: file " + filename + " has no data/header line.");
+    }
@@
-    if (line.find(',') == std::string::npos) {
+    if (line.find(',') == std::string::npos) {
         throw std::runtime_error("ERROR: file " + filename + " should contain the number of rows and columns in the format 'RR, CC'");
     }

Validation

• Run with a valid Semenov_PlanckOpacity.dat and confirm initialization still succeeds.
• Add a blank line before the first non-comment line; ensure no crash.
• Test a comment-only file and confirm clear exception message.