stringhelpers: remove redundant position variables
In both modified functions - findClose() and findCommaOrEnd() - the int
pos argument was used only until the loop, where it was replaced by a
local variable int a. This was error-prone as the disused argument pos
could be used instead of a
by mistake.
Note: I first suggested this refactoring in this comment in response to a mistaken use of pos
in place of a
.