`as_string=True` argument does not work in `plip.structure.preparation.PDBComplex.load_pdb()`

[AAriam]

Describe the bug
When setting as_string=True and passing the PDB content as a string, an error is raised.

To Reproduce
Using PDB-ID 3W32 as an example:

from plip.structure.preparation import PDBComplex

c=PDBComplex()
c.load_pdb(Path("3w32.pdb").read_text(), as_string=True)

raises:

OSError: No such file: 'HEADER    TRANSFERASE[/TRANSFERASE](http://localhost:8892/TRANSFERASE) INHIBITOR       07-DEC-12   3W32              
TITLE     EGFR KINASE DOMAIN COMPLEXED WITH COMPOUND 20A                        
COMPND    MOL_ID: 1;                                                            
COMPND   2 MOLECULE: EPIDERMAL GROWTH FACTOR RECEPTOR;                          
COMPND   3 CHAIN: A;                                                            
COMPND   4 FRAGMENT: KINASE DOMAIN, UNP RESIDUES 696-1022;                      
COMPND   5 SYNONYM: PROTO-ONCOGENE C-ERBB-1, RECEPTOR TYROSINE-PROTEIN KINASE   
COMPND   6 ERBB-1;                                                              
COMPND   7 EC: 2.7.10.1;                                                        
COMPND   8 ENGINEERED: YES                                                      
SOURCE    MOL_ID: 1;
...

Additional context
PLIP version: 2.4.0