[llvm] [Support] Add end/error to decode[US]LEB128AndInc (PR #90006)

[Alexandre Ganea via llvm-commits]

================
@@ -155,6 +155,12 @@ TEST(LEB128Test, DecodeInvalidULEB128) {
     EXPECT_NE(Error, nullptr);                                                 \
     EXPECT_EQ(0ul, Actual);                                                    \
     EXPECT_EQ(ERROR_OFFSET, ErrorOffset);                                      \
+    Value = reinterpret_cast<const uint8_t *>(VALUE);                          \
+    Error = nullptr;                                                           \
+    Actual = decodeULEB128AndInc(Value, Value + strlen(VALUE), &Error);        \
+    EXPECT_NE(Error, nullptr);                                                 \
+    EXPECT_EQ(0ul, Actual);                                                    \
+    EXPECT_EQ(ERROR_OFFSET, Value - reinterpret_cast<const uint8_t *>(VALUE)); \
----------------
aganea wrote:

```
Note: Google Test filter = LEB128Test.DecodeInvalidULEB128
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from LEB128Test
[ RUN      ] LEB128Test.DecodeInvalidULEB128
C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(167): error: Expected equality of these values:
  0u
    Which is: 0
  Value - reinterpret_cast<const uint8_t *>("")
    Which is: -5

C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(168): error: Expected equality of these values:
  1u
    Which is: 1
  Value - reinterpret_cast<const uint8_t *>("\x80")
    Which is: -167

C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(171): error: Expected equality of these values:
  9u
    Which is: 9
  Value - reinterpret_cast<const uint8_t *>("\x80\x80\x80\x80\x80\x80\x80\x80\x80\x02")
    Which is: -167

C:\src\git\llvm-project\llvm\unittests\Support\LEB128Test.cpp(172): error: Expected equality of these values:
  10u
    Which is: 10
  Value - reinterpret_cast<const uint8_t *>("\x80\x80\x80\x80\x80\x80\x80\x80\x80\x80\x02")
    Which is: -166

[  FAILED  ] LEB128Test.DecodeInvalidULEB128 (2 ms)
[----------] 1 test from LEB128Test (2 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (4 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] LEB128Test.DecodeInvalidULEB128

 1 FAILED TEST
```

https://github.com/llvm/llvm-project/pull/90006