Fix potential infinite loops in generators combined with section filter

The problem was that under specific circumstances, namely that none
of their children progressed, `GeneratorTracker` will not progress.
This was changed recently, to allow for code like this, where a
`SECTION` follows a `GENERATE` at the same level:

```cpp
SECTION("A") {}
auto a = GENERATE(1, 2);
SECTION("B") {}
```

However, this interacted badly with `SECTION` filters (`-c foo`),
as they could deactivate all `SECTION`s below a generator, and thus
stop it from progressing forever. This commit makes GeneratorTracker
check whether there are any filters active, and if they are, it checks
whether its section-children can ever run.

Fixes #2025

tests/CMakeLists.txt

@@ -160,6 +160,32 @@ set_tests_properties(FilteredSection-1 PROPERTIES FAIL_REGULAR_EXPRESSION "No te
 add_test(NAME FilteredSection-2 COMMAND $<TARGET_FILE:SelfTest> \#1394\ nested -c NestedRunSection -c s1)
 set_tests_properties(FilteredSection-2 PROPERTIES FAIL_REGULAR_EXPRESSION "No tests ran")
 
+add_test(
+  NAME
+    FilteredSection::GeneratorsDontCauseInfiniteLoop-1
+  COMMAND
+    $<TARGET_FILE:SelfTest> "#2025: original repro" -c "fov_0"
+)
+set_tests_properties(FilteredSection::GeneratorsDontCauseInfiniteLoop-1
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "inside with fov: 0" # This should happen
+    FAIL_REGULAR_EXPRESSION "inside with fov: 1" # This would mean there was no filtering
+)
+
+# GENERATE between filtered sections (both are selected)
+add_test(
+  NAME
+    FilteredSection::GeneratorsDontCauseInfiniteLoop-2
+  COMMAND
+    $<TARGET_FILE:SelfTest> "#2025: same-level sections"
+    -c "A"
+    -c "B"
+)
+set_tests_properties(FilteredSection::GeneratorsDontCauseInfiniteLoop-2
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "All tests passed \\(4 assertions in 1 test case\\)"
+)
+
 # AppVeyor has a Python 2.7 in path, but doesn't have .py files as autorunnable
 add_test(NAME ApprovalTests COMMAND ${PYTHON_EXECUTABLE} ${CATCH_DIR}/tools/scripts/approvalTests.py $<TARGET_FILE:SelfTest>)
 set_tests_properties(ApprovalTests