readpos: avoid static data

[ourairquality]

Allocate the large function local data on the heap.

[rtklibexplorer]

AI review:
One issue: fp leaks if either malloc() fails. The goto done; on malloc failure jumps past fclose(fp) (which only runs after the while loop on the success path), so done: frees poss/stas but never closes the file handle. Suggest either fclose(fp) before that goto done, or move the fclose(fp) up right after the read loop's initial setup so it's not gated on the malloc path at all.

[ourairquality]

Good point, fixed.