android build: enable asserts, and add sanity-check for it

Note that 0f541be6f1 added a warning log if asserts are disabled.
It is intentional that these two things are in separate files:
We always want to log that warning, even if someone is using electrum as a library.
However, in that latter case, I think it's fine not to sys.exit(), but leave the decision up to the library user.

Similar thinking when running from source: let's log the warning but don't sys.exit().

contrib/android/Dockerfile

@@ -179,8 +179,8 @@ RUN cd /opt \
     && git remote add sombernight https://github.com/SomberNight/python-for-android \
     && git remote add accumulator https://github.com/accumulator/python-for-android \
     && git fetch --all \
-    # commit: from branch accumulator/electrum_20210421d (note: careful with force-pushing! see #8162)
-    && git checkout "3c2750795ba93aa1a3e513a13c2ea2ac5bddba17^{commit}" \
+    # commit: from branch sombernight/electrum_20210421d (note: careful with force-pushing! see #8162)
+    && git checkout "ec82acf894822373ae88247658a233c77e76f879^{commit}" \
     && python3 -m pip install --no-build-isolation --no-dependencies --user -e .
 
 # build env vars

run_electrum

@@ -44,8 +44,9 @@ script_dir = os.path.dirname(os.path.realpath(__file__))
 is_pyinstaller = getattr(sys, 'frozen', False)
 is_android = 'ANDROID_DATA' in os.environ
 is_appimage = 'APPIMAGE' in os.environ
+is_binary_distributable = is_pyinstaller or is_android or is_appimage
 # is_local: unpacked tar.gz but not pip installed, or git clone
-is_local = (not is_pyinstaller and not is_android and not is_appimage
+is_local = (not is_binary_distributable
             and os.path.exists(os.path.join(script_dir, "electrum.desktop")))
 is_git_clone = is_local and os.path.exists(os.path.join(script_dir, ".git"))
 
@@ -62,6 +63,19 @@ if is_pyinstaller:
     # causes ImportErrors and other runtime failures). (see #4072)
     _file = open(sys.executable, 'rb')
 
+if is_binary_distributable:
+    # Ensure that asserts are enabled.
+    # Code *should not rely* on asserts being enabled. In particular, safety and security checks should
+    # always explicitly raise exceptions. However, this rule is mistakenly broken occasionally...
+    # In case we are a binary build, we know for a fact that we want the asserts, so enforce them.
+    # When running from source, defer to the user. (a warning is logged in __init__.py)
+    try:
+        assert False
+    except AssertionError:
+        pass
+    else:
+        sys.exit("Error: Running with asserts disabled, in a binary distributable! Please check build settings.")
+
 
 def check_imports():
     # pure-python dependencies need to be imported here for pyinstaller