Fix numeric with leading zero fractional (vapor#68)

* Create failing test

Numeric numbers with a fractional part with a leading zero (eg: 10.08) will be decoded from the database without the leading zero (ie: 10.80).

This is a serious issue which results in corrupted numeric values.

* Add padding of zeros to fractional portion of numericals

Author: dmonagle

Sources/PostgreSQL/Data/PostgreSQLData+String.swift

@@ -56,7 +56,8 @@ extension String: PostgreSQLDataConvertible {
                     if offset < metadata.weight.bigEndian + 1 {
                         integer += string
                     } else {
-                        fractional += string
+                        // Leading zeros matter with fractional
+                        fractional += fractional.count == 0 ? String(repeating: "0", count: 4 - string.count) + string : string
                     }
                 }
 

Tests/PostgreSQLTests/PostgreSQLConnectionTests.swift

@@ -213,7 +213,7 @@ class PostgreSQLConnectionTests: XCTestCase {
         params += Int16(1) // smallint
         params += Int32(2) // integer
         params += Int64(3) // bigint
-        params += String("123456789.123456789") // decimal
+        params += String("123456789.0123456789") // decimal
         params += Double(5) // numeric
         params += Float(6) // real
         params += Double(7) // double
@@ -238,7 +238,7 @@ class PostgreSQLConnectionTests: XCTestCase {
             try XCTAssertEqual(row.firstValue(forColumn: "smallint")?.decode(Int16.self), 1)
             try XCTAssertEqual(row.firstValue(forColumn: "integer")?.decode(Int32.self), 2)
             try XCTAssertEqual(row.firstValue(forColumn: "bigint")?.decode(Int64.self), 3)
-            try XCTAssertEqual(row.firstValue(forColumn: "decimal")?.decode(String.self), "123456789.123456789")
+            try XCTAssertEqual(row.firstValue(forColumn: "decimal")?.decode(String.self), "123456789.0123456789")
             try XCTAssertEqual(row.firstValue(forColumn: "real")?.decode(Float.self), 6)
             try XCTAssertEqual(row.firstValue(forColumn: "double")?.decode(Double.self), 7)
             try XCTAssertEqual(row.firstValue(forColumn: "varchar")?.decode(String.self), "8")