HPDF_FToA works improperly for small values

[Nekto89]

Broken in #187

#include <hpdf_utils.h>
#include <stdio.h>
#include <float.h>

int main() {
    HPDF_REAL value = 1e-15f;
    char buf[65];
    char* p = HPDF_FToA(buf, value, buf + 64);
    *p = '\0';
    printf("%s", buf);
    return 0;
}

In 2.4.3: 0.000000000000000'..-
in 2.3.0: 0

[maj0e]

Encountered the same problem, when trying to draw Text rotated by 90°. I called:

HPDF_Page_Concat(cos(PI/2), sin(PI/2), -sin(PI/2), cos(PI/2), 0, 0)

where on my computer I get cos(PI/2) == 6.12323e-17 and sin(PI/2) == 1.
Unfortunately the Text is not shown at all with that transformation matrix.
Setting small values to zero or using cosf(PI/2), which evaluates to "-4.37114e-08", works fine though, so I suspect it's related to this exact issue.

[bramton]

@Nekto89 The issue has now been resolved. The HPDF_INT64 used for storing the integer and fractional part was not sufficiently large.

@maj0e This is related to something else. The HPDF_FToA function is used for representing a float as a char array. It seems this is fixed by #255. If the issue persists, please create a new issue.