fix: handle ResumeFromDiskError gracefully in LoopProcessLogData (#7753)

When ReadFromBuffer returns ResumeFromDiskError, the function now:
- Attempts to read from disk if ReadFromDiskFn is available
- Checks if the client is still connected via waitForDataFn
- Waits for notification or short timeout before retrying
- Continues the loop instead of immediately returning the error

This fixes TestNewLogBufferFirstBuffer which was failing because the
function returned too early before data was available in the buffer.

weed/util/log_buffer/log_read.go

@@ -75,8 +75,36 @@ func (logBuffer *LogBuffer) LoopProcessLogData(readerName string, startPosition
 		}
 		bytesBuf, batchIndex, err = logBuffer.ReadFromBuffer(lastReadPosition)
 		if err == ResumeFromDiskError {
-			time.Sleep(1127 * time.Millisecond)
-			return lastReadPosition, isDone, ResumeFromDiskError
+		// Try to read from disk if readFromDiskFn is available
+		if logBuffer.ReadFromDiskFn != nil {
+			lastReadPosition, isDone, err = logBuffer.ReadFromDiskFn(lastReadPosition, stopTsNs, eachLogDataFn)
+				if err != nil {
+					return lastReadPosition, isDone, err
+				}
+				if isDone {
+					return lastReadPosition, isDone, nil
+				}
+			}
+
+			// CRITICAL: Check if client is still connected
+			if !waitForDataFn() {
+				// Client disconnected - exit cleanly
+				glog.V(4).Infof("%s: Client disconnected after disk read attempt", readerName)
+				return lastReadPosition, true, nil
+			}
+
+			// Wait for notification or timeout (instant wake-up when data arrives)
+			select {
+			case <-notifyChan:
+				// New data available, retry immediately
+				glog.V(3).Infof("%s: Woke up from notification after ResumeFromDiskError", readerName)
+			case <-time.After(10 * time.Millisecond):
+				// Timeout, retry anyway (fallback for edge cases)
+				glog.V(4).Infof("%s: Notification timeout after ResumeFromDiskError, polling", readerName)
+			}
+
+			// Continue to next iteration (don't return ResumeFromDiskError)
+			continue
 		}
 		if err != nil {
 			// Check for buffer corruption error