fix(func): no input, no output

An empty array made the Function API call TA-Lib with pointers one element
before its buffers: check_begidx answers length - 1, which is -1, so the
wrapper passed startIdx = endIdx = 0 and data + begidx. A function whose
lookback is zero reads and writes that element. That is 34 functions at
their default parameters, ACOS, ADD and OBV among them, plus any function
whose parameters give a zero lookback, such as MA(x, timeperiod=1), through
the Function, Abstract, pandas and polars paths alike. The heap corruption
may abort the interpreter later, on an unrelated free, or go unnoticed.
Stream opens are not affected; they raise InsufficientHistory first.

When it started: 0.4.27, tagged 2023-07-13. Commit 02de3a3 ("don't throw
exceptions on all nan input", CHANGELOG "[FIX]: Don't throw exceptions when
inputs are all NaN") replaced check_begidx's `raise Exception("inputs are
all NaN")` with `return length - 1`. An empty array takes that same branch,
so until then it raised; since then it has reached TA-Lib with begidx -1.
Every release since has it, through 0.8.0.

Every wrapper now returns its outputs as empty arrays, before check_begidx,
the lookback or TA-Lib are reached. Nothing else changes for an empty input:
types, dtypes and tuple layout match the non-empty path, and for valid
parameters the results are identical to before across func, the pandas and
polars wrappers, and abstract with dict, pandas and polars DataFrame inputs,
for all 201 functions. An invalid parameter on an empty input now returns
empty outputs instead of TA_BAD_PARAM: there is nothing to compute.

The test runs in a child process with the empty inputs right after an
inaccessible page, so a read before the buffer faults at once. It fails on
the previous code with SIGSEGV. It is skipped on Windows, where the guard
would need VirtualProtect and no CI runs the tests.

Claude-Session: https://claude.ai/code/session_01TuVjx2Q5urdmwi5opzfCp8

Author: mario4tier

CHANGELOG

@@ -24,6 +24,13 @@
   ``real`` and ``integer``; they are ``supertrend`` and ``trend``, the names
   ``abstract.Function('SUPERTREND').output_names`` already reported.
 
+- [FIX]: An empty array given to a function whose lookback is zero, such as
+  ``talib.ACOS`` or ``talib.MA(x, timeperiod=1)``, made TA-Lib read and write
+  one element outside the buffers, which could crash the interpreter later or
+  corrupt memory silently.  An empty input now returns empty outputs without
+  calling TA-Lib, whatever the function and its parameters.  The bug dates from
+  0.4.27.
+
 0.8.0
 =====