tools: LogAnalyzer fixes to work with pipes as input

seek is not supported on pipes (and not needed in this case)
tell is also not supported, so count bytes on our own

Tools/LogAnalyzer/DataflashLog.py

@@ -287,11 +287,13 @@ class DataflashLog:
             f = open(self.filename, 'r')
         if f.read(4) == '\xa3\x95\x80\x80':
             raise Exception("Unable to parse binary log files at this time, will be added soon")
-        f.seek(0)
+
         lineNumber = 0
         knownHardwareTypes = ["APM", "PX4", "MPNG"]
+        numBytes = 0
         for line in f:
             lineNumber = lineNumber + 1
+            numBytes += len(line) + 1
             try:
                 #print "Reading line: %d" % lineNumber
                 line = line.strip('\n\r')
@@ -389,7 +391,8 @@ class DataflashLog:
 
         # gather some general stats about the log
         self.lineCount  = lineNumber
-        self.filesizeKB = f.tell() / 1024.0
+        self.filesizeKB = numBytes / 1024.0 # For data that comes from a process pipe, filesize is not supported
+
         # TODO: switch duration calculation to use TimeMS values rather than GPS timestemp
         if "GPS" in self.channels:
             # the GPS time label changed at some point, need to handle both