Possible bug in array handling after end of input (END handler)

[Christian Schmidt]

Dear gawk maintainers,

I stumbled across an unexpected behavior where a for (var in array)
construct encounters each array element twice if called from an END handler.

A small test case:

=== begin t.awk ===
function dump() {
    for (i in vars) printf ("%s:%s ", i, vars[i]);
    print;
    delete vars;
}
(NF == 0) { dump(); }
(NF > 0) {
    for (i=1; i<=NF; i++) {
        split ($i, a, /:/);
        vars[a[1]] = a[2];
    }
}
END { dump(); }
=== end t.awk ===
=== begin data.txt ===
a:1 b:2
c:4

a:2 b:5 c:3
=== end data.txt ===

Resulting output:
awk -f t.awk data.txt
a:1 b:2 c:4
a:2 b:5 c:3 a:2 b:5 c:3

awk --version
GNU Awk 5.1.0, API: 3.0

If another empty line is added to the end of data.txt, the output
changes as expected:
awk -f t.awk data.txt
a:1 b:2 c:4
a:2 b:5 c:3
<blank line>

Best regards and looking forward for your help,
Chris

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