fix reading of nrstart and ncstart in CCP4 format

- close #57
- thanks to @Digp for excellent bug report with data and solution

Author: orbeckst

CHANGELOG

@@ -23,6 +23,7 @@ The rules for this file:
   * Fixed reading in DX files containing scientific notation (PR #52)
   * Added missing floordivision to Grid (PR #53)
   * fix test on ARM (#51)
+  * fix incorrect reading of ncstart and nrstart in CCP4 (#57)
 
   Changes (do not affect user)
 

gridData/CCP4.py

@@ -177,7 +177,7 @@ class CCP4(object):
             3: 'Transform of Complex Integer*2',
             4: 'Transform of Complex Reals',
             5: '0',
-        }), Record('ncstart', 'I'), Record('nrstart', 'I'),
+        }), Record('ncstart', 'i'), Record('nrstart', 'i'),
         Record('nsstart', 'I'), Record('nx', 'I'),  # Number of gridpoints.
         Record('ny', 'I'), Record('nz', 'I'), Record('xlen', 'f'),  # Angstroms.
         Record('ylen', 'f'), Record('zlen', 'f'), Record('alpha', 'f'),  # Degrees.