Fix whitespace.
android: Fix crash when external storage is missing.
android: Add note about NDK targets to ReadMe.
Ensure that TIFFs with resolution set to zero get sane values.

This is required for XPS, as otherwise images can be completely
omitted.
Fix 695467: Add and use fz_ftoa function (like dtoa but with floats).

The dtoa function is for doubles (which is what MuJS uses) but for MuPDF
we only need and want float precision in our output formatting.
Fix 695501: check upper and lower bounds of CMap when computing ToUnicode.

When inverting the CMap to create a ToUnicode, first check the actual
range of input characters rather than relying only on the codespace
range list.
Update to latest MuJS.