use an overflow check instead of a hard coded value for ETA

docs/changes.txt

@@ -25,6 +25,7 @@
 - Fixed a memory problem that occured when the OpenCL folder was not found and e.g. the shared and session folder were the same
 - Fixed the version number used in the restore file header
 - Fixed the parsing of command line options. It doesn't show two times the same error about an invalid option anymore.
+- Fixed the estimated time value whenever the value is very large and overflows
 
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 ## Improvements