strconv: avoid panic on invalid call to FormatFloat
Calling FormatFloat with an invalid value of fmt is expected
to return a string containing '%' and the input fmt character.
Since even before Go 1.0, the code has been panicking in the
case where prec=0.
Fixes #52187
Change-Id: I74fec601eedb7fe28efc5132c4253674661452aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/402817
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com> Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Emmanuel Odeke <emmanuel@orijtech.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>