refactor: Fix unreachable code in init arg checks

Building with -Wunreachable-code-loop-increment causes a warning
due to always returning on the first iteration of the loop that
outputs errors on invalid args.

Collect all errors, and output them in a single error message
after the loop completes, resolving the warning and avoiding
popup hell by outputting a seperate message for each error.

src/init.cpp

@@ -964,17 +964,27 @@ bool AppInitParameterInteraction()
 
     // also see: InitParameterInteraction()
 
-    // Warn if network-specific options (-addnode, -connect, etc) are
+    // Error if network-specific options (-addnode, -connect, etc) are
     // specified in default section of config file, but not overridden
     // on the command line or in this network's section of the config file.
     std::string network = gArgs.GetChainName();
+    bilingual_str errors;
     for (const auto& arg : gArgs.GetUnsuitableSectionOnlyArgs()) {
-        return InitError(strprintf(_("Config setting for %s only applied on %s network when in [%s] section."), arg, network, network));
+        errors += strprintf(_("Config setting for %s only applied on %s network when in [%s] section.") + Untranslated("\n"), arg, network, network);
+    }
+
+    if (!errors.empty()) {
+        return InitError(errors);
     }
 
     // Warn if unrecognized section name are present in the config file.
+    bilingual_str warnings;
     for (const auto& section : gArgs.GetUnrecognizedSections()) {
-        InitWarning(strprintf(Untranslated("%s:%i ") + _("Section [%s] is not recognized."), section.m_file, section.m_line, section.m_name));
+        warnings += strprintf(Untranslated("%s:%i ") + _("Section [%s] is not recognized.") + Untranslated("\n"), section.m_file, section.m_line, section.m_name);
+    }
+
+    if (!warnings.empty()) {
+        InitWarning(warnings);
     }
 
     if (!fs::is_directory(GetBlocksDir())) {

src/util/translation.h

@@ -23,6 +23,11 @@ struct bilingual_str {
         translated += rhs.translated;
         return *this;
     }
+
+    bool empty() const
+    {
+        return original.empty();
+    }
 };
 
 inline bilingual_str operator+(bilingual_str lhs, const bilingual_str& rhs)

test/functional/feature_config_args.py

@@ -71,7 +71,7 @@ class ConfArgsTest(BitcoinTestFramework):
         with open(inc_conf_file2_path, 'w', encoding='utf-8') as conf:
             conf.write('[testnet]\n')
         self.restart_node(0)
-        self.nodes[0].stop_node(expected_stderr='Warning: ' + inc_conf_file_path + ':1 Section [testnot] is not recognized.' + os.linesep + 'Warning: ' + inc_conf_file2_path + ':1 Section [testnet] is not recognized.')
+        self.nodes[0].stop_node(expected_stderr='Warning: ' + inc_conf_file_path + ':1 Section [testnot] is not recognized.' + os.linesep + inc_conf_file2_path + ':1 Section [testnet] is not recognized.')
 
         with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
             conf.write('')  # clear