set errno=0 before strtoX calls

To detect conversion failure after calls to functions like `strtod`, one
can check `errno == ERANGE`. These functions are not guaranteed to set
`errno` to `0` on successful conversion, however. Manual manipulation of
`errno` can likely be avoided by checking that the output pointer
differs from the input pointer, but that's not how other locations, such
as parse.c:139, handle this issue; they set errno to 0 prior to
executing the function.

For every place I could find a strtoX function with an ERANGE check
following it, set `errno = 0;` prior to executing the conversion
function.

Signed-off-by: Kyle Lippincott <spectral@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-json-writer.c

@@ -415,6 +415,7 @@ static void get_i(struct line *line, intmax_t *s_in)
 
 	get_s(line, &s);
 
+	errno = 0;
 	*s_in = strtol(s, &endptr, 10);
 	if (*endptr || errno == ERANGE)
 		die("line[%d]: invalid integer value", line->nr);
@@ -427,6 +428,7 @@ static void get_d(struct line *line, double *s_in)
 
 	get_s(line, &s);
 
+	errno = 0;
 	*s_in = strtod(s, &endptr);
 	if (*endptr || errno == ERANGE)
 		die("line[%d]: invalid float value", line->nr);