editors/nvi2: Fix "move forward paragraphs" (}) with numeric prefix

Two github issues identified the same problem:

https://github.com/lichray/nvi2/issues/118
https://github.com/lichray/nvi2/pull/119

For example typing "}" three times on this sample text:

.PP
1
.PP
2
.PP
3
.PP
4
.PP
5
.PP
6

moves the cursor 3 paragraphs but typing "3}" (correct) moves the
cursor 5 paragraphs ((2 * N) - 1, incorrect).

Reported by: Walter Alejandro Iglesias, Zhihao Yuan