py/parsenum: Fix parsing complex literals with negative real part.

If a complex literal had a negative real part and a positive imaginary
part, it was not parsed properly because the imaginary part also came out
negative.

Includes a test of complex parsing, which fails without this fix.

Co-authored-by: ComplexSymbol <141301057+ComplexSymbol@users.noreply.github.com>
Signed-off-by: Jeff Epler <jepler@gmail.com>

py/parsenum.c

@@ -227,13 +227,13 @@ mp_obj_t mp_parse_num_float(const char *str, size_t len, bool allow_imag, mp_lex
 
     const char *top = str + len;
     mp_float_t dec_val = 0;
-    bool dec_neg = false;
 
     #if MICROPY_PY_BUILTINS_COMPLEX
     unsigned int real_imag_state = REAL_IMAG_STATE_START;
     mp_float_t dec_real = 0;
-parse_start:
+parse_start:;
     #endif
+    bool dec_neg = false;
 
     // skip leading space
     for (; str < top && unichar_isspace(*str); str++) {

tests/float/complex1.py

@@ -12,9 +12,11 @@ print(complex("1.2j"))
 print(complex("1+j"))
 print(complex("1+2j"))
 print(complex("-1-2j"))
+print(complex("-1+2j"))
 print(complex("+1-2j"))
 print(complex(" -1-2j "))
 print(complex(" +1-2j "))
+print(complex(" -1+2j "))
 print(complex("nanj"))
 print(complex("nan-infj"))
 print(complex(1, 2))