Bug in "gsl_cdf_beta_Pinv" and return NaN

[Mehdi Taghizadeh]

Hope you are doing well,
-The version number of GSL: 1.16 and also, 2.4-Hardware and operating system: 
Lenovo E531, Windows 10 x64-The compiler used: C++ program in Visual studio 
2015 enterprise, Release and Debug.-A description of the bug behavior:For some 
values of P, the inverse beta function fails to converge and return NaN. 
Here are the inputs and the corresponding results of the beta inverse function 
in MATLAB.a = 9.15     b = 657.69     P = 0.957   gsl= NaN   MATLAB = 0.0223
a = 0.812   b = 337.12     P = 0.658   gsl= NaN   MATLAB = 0.0025  
a = 1.62     b = 1983.37   P = 0.704   gsl= NaN   MATLAB = 0.0010
a = 1.07     b = 242.92     P = 0.884.  gsl= NaN   MATLAB = 0.0093 Also, this 
issue appeared in the inverse function of Gamma distribution, So, I think it 
all goes back to an issue in the Gamma function because it is used for both 
distributions.   
Please let me know if you have any suggestions to fix this bug. Many thanks. 
Thanks in advance,Mehdi Tahgizadeh