Fix negative integers rendered as floats in CSV output

The numeric fallback chain as_u64 -> as_f64 caused negative integers
to fail as_u64 and fall through to as_f64, producing "-1.0" instead of
"-1". Insert as_i64 between as_u64 and as_f64 to handle negative integers
correctly.

Author: 514sid

src/commands/mod.rs

@@ -89,6 +89,8 @@ where
                                 b.to_string()
                             } else if let Some(n) = fv.as_u64() {
                                 n.to_string()
+                            } else if let Some(n) = fv.as_i64() {
+                                n.to_string()
                             } else if let Some(n) = fv.as_f64() {
                                 n.to_string()
                             } else if fv.is_null() {