empty lines in mol2

Some mol2 files have empty lines between blocks. We need to remove them from the block content of the previous one.

biopandas/mol2/pandas_mol2.py

@@ -180,7 +180,7 @@ def _get_atomsection(mol2_lst):
             if s.startswith("@<TRIPOS>ATOM"):
                 first_idx = idx + 1
                 started = True
-            elif started and s.startswith("@<TRIPOS>"):
+            elif started and s.startswith("@<TRIPOS>") or not s.strip():
                 last_idx_plus1 = idx
                 break
         if first_idx is None: