Added check to make sure hash is valid hex (#153)

src/project_parser.cpp

@@ -550,6 +550,14 @@ Project::Project(const Project *parent, const std::string &path, bool build) : p
                         algo.push_back(ch);
                     }
                     key = "URL_HASH";
+                    if (value.empty()) {
+                        throw_key_error("Empty hash value", argItr.first, argItr.second);
+                    }
+                    for (char c : value) {
+                        if (!std::isxdigit(c)) {
+                            throw_key_error("Hash value must be a hex string", argItr.first, argItr.second);
+                        }
+                    }
                     value = algo + "=" + value;
                 } else if (key == "hash") {
                     key = "URL_HASH";