Health API: Fix for MissingContentDir wrong

[infeo]

Per spec, the content directory in cipher space consists of 32 characters representing the SHA1 hash of the directory id. (for an example, see spec)

The result MissingContentDir indicates, that for an existing dirId, the content dir is missing. The fix is to create the directory.
But looking at the code to fix it, it is wrongly implemented:

cryptofs/src/main/java/org/cryptomator/cryptofs/health/dirid/MissingContentDir.java

Line 52 in 2f42f3c

Path dirPath = pathToVault.resolve(Constants.DATA_DIR_NAME).resolve(dirIdHash.substring(0, 2)).resolve(dirIdHash.substring(2, 30));

Java substring method takes two indices, not a start index and a length.