Correct position on invalid files ending without value

Previously it would be on the next line:

    % tomlv <(print 'a=')
    Error in '/proc/self/fd/11': toml: error: expected value but found '\n' instead

    At line 2, column 3:

          1 | a=
          2 |
                ^

error_test.go

@@ -51,8 +51,23 @@ At line 2, column 5-15:
       1 | # Date cannot end with trailing T
       2 | d = 2006-01-30T
               ^^^^^^^^^^^`},
-	}
 
+		{"key/without-value-1.toml", `
+toml: error: expected '.' or '=', but got '\n' instead
+
+At line 1, column 4:
+
+      1 | key
+             ^`},
+		// Position looks wonky, but test has trailing space, so it's correct.
+		{"key/without-value-2.toml", `
+toml: error: expected value but found '\n' instead
+
+At line 1, column 7:
+
+      1 | key = 
+                ^`},
+	}
 	fsys := tomltest.EmbeddedTests()
 	for _, tt := range tests {
 		t.Run(tt.test, func(t *testing.T) {

lex.go

@@ -492,6 +492,9 @@ func lexKeyEnd(lx *lexer) stateFn {
 		lx.emit(itemKeyEnd)
 		return lexSkip(lx, lexValue)
 	default:
+		if r == '\n' {
+			return lx.errorPrevLine(fmt.Errorf("expected '.' or '=', but got %q instead", r))
+		}
 		return lx.errorf("expected '.' or '=', but got %q instead", r)
 	}
 }
@@ -560,6 +563,9 @@ func lexValue(lx *lexer) stateFn {
 	if r == eof {
 		return lx.errorf("unexpected EOF; expected value")
 	}
+	if r == '\n' {
+		return lx.errorPrevLine(fmt.Errorf("expected value but found %q instead", r))
+	}
 	return lx.errorf("expected value but found %q instead", r)
 }