F file read error

Summary

See #30 (closed). Having an empty path for the certificate leads to a vanilla basic iostream error

Focus

The basic exception is caught and changed into a slightly more precise Exception with error code.

Test Environment

e.g. set cert path to empty string and try to connect

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include/caosdb/status_code.h

@@ -62,6 +62,7 @@ enum StatusCode {
   FILE_UPLOAD_ERROR = 35,
   FILE_DOWNLOAD_ERROR = 36,
   ENUM_MAPPING_ERROR = 37,
+  FILE_CANNOT_BE_READ = 38,
   OTHER_CLIENT_ERROR = 9999,
 };