clear error if pandas isn't importable, test without pandas installed

Author: ngoldbaum

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
       - name: Install build and test dependencies
         run: |
           pip install -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy
-          python -m pip install -U pip build pytest unyt wheel meson ninja meson-python patchelf
+          python -m pip install -U pip build pytest unyt wheel meson ninja meson-python patchelf pandas
       - name: Install asciidtype
         working-directory: asciidtype
         run: |
@@ -78,3 +78,5 @@ jobs:
         working-directory: stringdtype
         run: |
           ASAN_OPTIONS=detect_leaks=false LD_PRELOAD=/usr/lib/gcc/x86_64-linux-gnu/11/libasan.so pytest -s -vvv --color=yes
+          pip uninstall pandas
+          ASAN_OPTIONS=detect_leaks=false LD_PRELOAD=/usr/lib/gcc/x86_64-linux-gnu/11/libasan.so pytest -s -vvv --color=yes

stringdtype/stringdtype/src/dtype.c

@@ -600,6 +600,7 @@ init_string_dtype(void)
     }
     else {
         PandasStringDType = StringDType;
+        PyErr_Clear();
     }
 
     for (int i = 0; casts[i] != NULL; i++) {