chore: fix compiler warnings

[mfenniak]

Warning in python.c:

src/python.c:941:9: warning: variable 'isNull' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
  941 |                                 if (es == NULL)
      |                                     ^~~~~~~~~~
src/python.c:948:23: note: uninitialized use occurs here
  948 |                                 newqual->isnull = isNull;
      |                                                   ^~~~~~
src/python.c:941:5: note: remove the 'if' if its condition is always true
  941 |                                 if (es == NULL)
      |                                 ^~~~~~~~~~~~~~~
  942 |                                 {
src/python.c:925:15: note: initialize the variable 'isNull' to silence this warning
  925 |                 bool            isNull;
      |                                       ^
      |                                        = false
1 warning generated.

Warning in query.c:

src/query.c:70:8: warning: variable 'i' set but not used [-Wunused-but-set-variable]
   70 |         int                     i = 0;
      |                                 ^
1 warning generated.