constify missing catch cases

- ensure all missing catch cases are constant where possible

src/bitcoind.cpp

@@ -109,7 +109,7 @@ bool AppInit(int argc, char* argv[])
         // Check for -testnet or -regtest parameter (Params() calls are only valid after this clause)
         try {
             SelectParams(ChainNameFromCommandLine());
-        } catch(std::exception &e) {
+        } catch (const std::exception& e) {
             fprintf(stderr, "Error: %s\n", e.what());
             return false;
         }