#26545 Fix: same .tsv file, get different data-frame structure using engine 'python' and 'c' 
- [x] closes #26545
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

BugFix:
When using `engine='python'`, columns were handled incorrectly if the first header had in the bom.

Bug:
```
In [1]: import pandas as pd                                                             

In [2]: pd.read_csv('test.txt', engine='python', delimiter='\t')              
Out[2]: 
Empty DataFrame
Columns: [Project ID]
Index: []

In [3]: pd.read_csv('test.txt', engine='python', delimiter='\t').shape        
Out[3]: (0, 1)

In [4]: pd.read_csv('test.txt', delimiter='\t')                               
Out[4]: 
Empty DataFrame
Columns: [Project ID, Project Name, Product Name]
Index: []

In [5]: pd.read_csv('test, delimiter='\t').shape                         
Out[5]: (0, 3)
```
Fix:

```
In [1]: import pandas as pd                                                             

In [2]: pd.read_csv('test.txt', engine='python', delimiter='\t')              
Out[2]: 
Empty DataFrame
Columns: [Project ID, Project Name, Product Name]
Index: []

In [3]: pd.read_csv('test.txt', engine='python', delimiter='\t').shape        
Out[3]: (0, 3)

In [4]: pd.read_csv('test.txt', delimiter='\t')                               
Out[4]: 
Empty DataFrame
Columns: [Project ID, Project Name, Product Name]
Index: []

In [5]: pd.read_csv('test, delimiter='\t').shape                         
Out[5]: (0, 3)
```