JSON start point fix in multiproc usecase

Change-Id: I84317af41ec0828f08bb2d45803515738167e77a


[ROCm/rocprofiler commit: 60c106a07d]

projects/rocprofiler/bin/tblextr.py

@@ -572,8 +572,12 @@ csvfile = ''
 begin_ts_file = indir + '/begin_ts_file.txt'
 if os.path.isfile(begin_ts_file):
   with open(begin_ts_file, mode='r') as fd:
-    START_US=int(fd.readline()) / 1000
-    print('Appilcation START-ts found (' + str(START_US) + 'us)')
+    ind = 0
+    for line in fd.readlines():
+      val = int(line) / 1000
+      if ind == 0 or val < START_US: START_US = val
+      ind += 1
+  print('START timestamp found (' + str(START_US) + 'us)')
 
 if re.search(r'\.csv$', outfile):
   csvfile = outfile