Ensure that loggers never yield when processing log data.

Doing so would break fundamental assumptions about not yielding within low level code that might very well perform logging.

source/vibe/core/log.d

@@ -1056,13 +1056,17 @@ unittest { // ensure arguments are evaluated lazily
 }
 
 private struct LogOutputRange {
+	import vibe.core.core : yieldLock;
+
 	LogLine info;
 	ScopedLock!Logger* logger;
 
 	@safe:
 
 	this(ref ScopedLock!Logger logger, string file, int line, LogLevel level)
 	{
+		auto l = yieldLock();
+
 		() @trusted { this.logger = &logger; } ();
 		try {
 			() @trusted { this.info.time = Clock.currTime(UTC()); }(); // not @safe as of 2.065
@@ -1088,6 +1092,8 @@ private struct LogOutputRange {
 
 	void finalize()
 	{
+		auto l = yieldLock();
+
 		logger.endLine();
 	}
 
@@ -1096,6 +1102,8 @@ private struct LogOutputRange {
 		if (text.empty)
 			return;
 
+		auto l = yieldLock();
+
 		if (logger.multilineLogger) {
 			logger.put(text);
 		} else {